So confused

but as you say your other daughter has a larger house, and there are 3 adults there, to look after 3 children, if your GS stays there.
i know it's not ideal, but it sounds a better set-up than you travelling all that distance and put yourself at risk.
they are a generation younger. you are extra vulnerable.
the natural father of the 2 children is staying there with them. then there is your other daughter and her partner.
3 adults, 3 children.
you cannot solve all your daughter's problems.
if long-term care / support for her child is needed that would have to be arranged/agreed by social services.
you need to look after you.

Could she come and stay with you for a while?

Health visitors will be working remotely at the moment

Can you get in touch with her GP to set up a health visitor ?

Has your daughter been in touch with her doctor?
It seems that she needs a bit more help than you would be able to give, and you would be putting yourself at risk.

Is this an issue since the virus, or did she struggle before?

I'm shielding for asthma and fixed airway disease and in extremely clinically vulnerable category. It's not just next few days I'm concerned about my youngest but longer term. She's already depressed and I'm worried for her and my DGS. She lives in a one bed flat with no where for me to sleep. Middle daughter has bigger house but has her own two childrrn, her partner and children's dad who lost his home during covid. Logically there's a house full of people to help so I should stay put. Just feel I want to help both my daughters.

I was also trying to shield, didn't have a letter but given my medical conditions include a damaged lung I thought it best to shield. However, I have a daughter with learning disability and is also disabled living on her own in a small town. Its been at least once a week I had to travel across to see her and the last time call an ambulance as she had a suspected stroke. I take all the precautions I can including changing all my clothes and putting them in the machine when I get back. However, yours is different in that you will have to stay which you feel very uneasy about. Why not have a chat with your doctor and see if he thinks it would be OK as he knows the details of your medical history. They are saying we can stop shielding in August, which is not so far away.

First welcome lynn this is a worrying time for you

It really depends what your reason for shielding is?
I m not sure I understand ....if your daughter is a single mum with one small child why would you say you d be in a house with five people from two households Wouldn’t you just be in her house/flat/rooms with the little one until she gets back from hospital