Although she leaves school in June, child benefit and the child element of UC will run on until the end of August, you'll get a message from UC asking you to confirm what she is doing.
If she does decide to carry on at college, you can get child benefit and UC for her as your dependent until the end of August following her 19th birthday.
You can claim the caring element of UC - UC allows you work full time providing you still provide 35 hours of care a month, this is worth £185 a month to you, if you haven't done this yet, do it ASAP.
From September, she'll need her own UC claim, if you're her appointee, you'll need to make the claim. Make sure she reports her health issues, for long term health conditions, ask the GP for a fit note for 3 months +, this saves having to keep going back. She'll have a work capability assessment, very similar to the PIP assessment, but based on capability for work rather than care and mobility needs.
The work capability process takes about 3 months, if she's placed in the limited capability for work and related activity group, she will receive an additional element, currently £390 a month.