There are many well-evidenced approaches to dealing with both of these problems: ACT wouldn’t claim to be the only one, or better than all the others, but it does seem to be useful for a lot of people, and copes well with multiple simultaneous problems. 

ACT is an approach that recognizes that genuinely bad things happen in peoples’ lives, and that strong and unwanted thoughts, feelings and sensations are an inevitable consequence. They’re not symptoms or signs of dysfunction, but are simply the human mind and body doing what they’re designed to do. Instead of trying to reason our way out of the thoughts or get rid of the feelings (and in chronic illness and grief maybe that’s not possible), ACT emphasises learning to notice what’s happening, let go of the unhelpful struggle against those internal experiences and instead engage in meaningful activity. That way, we can live fulfilling lives even in the presence of the suffering that life can bring.

One of the nice things about ACT is it can be used as a way of achieving other therapeutic goals – for instance, increasing self-compassion and accepting compassion from others. For some people, it’s not enough that they understand why that might be helpful, and are motivated to do so. Sometimes – in the moment – feelings of discomfort, shame, guilt or anxiety will surface, and/or thoughts of not being deserving, being weak and so on. That can lead people to pull away from the very self-compassionate behaviors they were trying to learn.

ACT techniques of making room for those emotions, recognizing those thoughts and defusing/unhooking from them can be used in the service of doing this thing (increasing self-compassion, say), so moving towards valued living.

Experiences of grief can be so variable, can’t they? I have certainly worked with people where suffering has increased over time, and looking back the reasons have differed for all of them: sometimes it has been more about dealing with the experience of loss, missing the person, regrets and so on, and sometimes more about their interaction with the world going forward, and attempting to build a worthwhile life even in the absence of the person who died. I will often try to work on both those aspects alongside each other (in line with Stroebe’s ‘Dual Process Model’ of grief, if you’re familiar with that), emphasising what mattered most in their relationship to the deceased (for good or ill), what that says about the grieving person’s values, and look at ways of building some small element of those values into their new life. Sometimes, this is also a way of honouring the person who died, sometimes a way of continuing a bond with them. Also taking care to notice any guilty thoughts about ‘moving on’, and being careful not to move too fast.

This is one of the hardest of situations. It’s difficult enough to face our own suffering and mortality, but to face that of our child is likely to be so much worse.

It’s tempting to say the situation is made even harder by having to continue parenting in that situation, but I’d argue that this points to a way of coping. Heavy as that responsibility is, focussing upon parenting can reduce some of the helplessness that is felt: even if the outcomes cannot be guaranteed, people do have some control over their behaviour. As well as general ACT skills for dealing with inevitable really difficult thoughts and feelings  I’d be examining their Values around parenting – what for you are the qualities of action that define the parent you want to be? Whatever you find – e.g. being caring, being dependable, being patient or any other – I would look at how their current behaviour already reflects that, as well as looking to find other small and manageable ways of acting in that manner.

None of that is going make the situation OK, yet it can help people do what matters to them at one of the most important moments of their lives.

ACT has proved a popular intervention in chronic pain groups and is increasingly included in recommended treatment guidelines. It is one of the World Health Organization's recommended approaches for chronic pain in young people and some specialist centers, such as the Bath Centre for Pain Service in the UK, organize their group treatment programs around an ACT framework.

Briefly, key ACT processes include: values work around the life the young person would want to be leading; exposure exercises to consensual physical rehabilitation seen as committed action in pursuit of those values; coping with the catastrophic pain-related thoughts and feelings that can arise, especially in response to physical pain experience; and attention to the developing sense of self beyond unhelpful self-stories. Group interactions help, as meeting others in similar situations can support all of these processes. Additionally, involvement with parents and caregivers of the young people is seen as vital to address their own stresses, turmoil and behavioral responses, and the way they partly shape the young person’s coping.

While it’s tempting to say that ‘all of them play a part’, reflecting on my experience of people like this, I think the Values work has been a key driver, partly to (gently and respectfully) build an alternative to the sense of pointless and hopelessness that often shows up. I often do some looking back – what were the sweet spots in life before? What do they tell us about what has mattered in your life? Being ready for strong sadness and regret emerging, how can we build some small element of those qualities into your life now? Difficult thoughts and feelings will show up when you do that – how are we going to support you in making room for them? The ‘dropping anchor’ technique (easily findable online) can help a person pull back from being lost in these thoughts, memories and feelings.

Techniques around awareness (noticing internal states especially) and defusion may help re-establish better eating and sleeping patterns that will support any other health- or grief-related adjustments. Where possible, I like to get as clear a picture as possible of what’s going on with the physical health problem for this particular person, as that context may shape available behaviours and their consequences differently than a healthier person may experience.

As always in ACT, the key question would be how this particular individual is responding to her fatigue and her pain – we could say those experiences are part of her context, and we are interested in how she has learned to respond to them, and what are the consequences helpful and unhelpful, short-term and long? 

In a situation like this, I think I would be particularly looking out for a few things. Adolescence is a time of exploring the world and working out what kind of person you want to be (including what you value). All of that is going to be strongly influenced by fatigue and pain, and the isolation from peers that may bring. Doing the work of adolescence within these constraints may benefit from support: there’s a particular form of ACT designed for children, adolescents and young people called DNA-V which gives good tools for this https://dnav.international/dna-v-for-youth/ 

It would also be a mistake (as it always is) to disregard the content of the thoughts and feelings in a rush to defusion and acceptance: often (and especially here) we may be dealing with reactions driven by self-protection against past exacerbations of pain and fatigue and fear of catastrophic worsening.  Any exposure work regarding increased amount or range of activity must be respectful of those internal warning voices, maybe seeing them as advisers wanting to keep the young person safe, and also possibly getting in the way sometimes of trying things that might improve quality of life.