What does one still have to do when on UC and with "Fit Note" from GP?

Hello!,
Sorry if this is the wrong place, I've looked in various guides and cannot find any answers, I sent in an email and was advised to ask here>
I am writing on behalf of my sister who claims UC. We filled in a Capability Questionnaire for her and sent it back over a month ago. She is not at all well; she has heart problems, learning difficulties, very bad oedema of one leg, has had 3 TIAs (in the last year) which have affected her balance et. etc. Her GP has been signing her off every 3 months (issuing a Fit Note!), despite all this the job Centre insisted she visit (an hour's journey away) every fortnight and also visit Redcap (?) every 2 weeks, again 1 hr away. She cannot cross roads safely on her own as her TIAs have affected her balance and she falls over when she turns her head, this is totally unsafe making her do this. finally the job centre has accepted phone appointments instead, but Redcap still want her to visit. She has now been passed to the Careers Advice (she's 48 and had a good job until too ill to work)!
Surely with a Fit Note she should not have to keep doing this? I used your guides to help her fill in the form, but she forgot to send it for another month (I live a long way away).
She also suffers from depression and anxiety which is made 100x worse by their insistence. She keeps calling me saying that she "cannot do this any more". Can they really expect her to travel when it is unsafe for her to do so and puts her in bed for several days afterwards?
I don't know what else I can do to help. Our brother has been appointed her guardian as she cannot cope with money (she has been the victim of so many scams as she believes everyone). I am the one she turns to for love and mental support.
Can you please advise?
Many Thanks
Sally