@Treefy Get her to get in contact with her university Disability Service, she can do this before results day etc. Did she click she had a disability when applying on UCAS? If yes then they should have already contacted her, so get her to check her emails and see if she missed it.
If not she can go on their website and email them or fill in an online form. Then they'll make her a personalised learning support plan. She will have to give them evidence (but if she's in the process of diagnosis it should count), then she can have an online meeting go through anything she's struggling with and the support she'll get e.g help with writing longer assesments, tell lectures to give her extra support with presentations. She'll also likely be able to get extra time, rest breaks during exams, espeically if she had them at college. But even if she didn't, each university decides on their own, so much more flexible than A-levels etc. They can also, once she starts, do a referral to university counselling service, for short to medium term therapy. Then I'm assuming she's moving out for uni, she'll need a new GP Practice and then get her to go to them, say how shes been struggling and ask for a referral to adult mental health services for long-term therapy. Ask if she can have something other than CBT because it often doesn't help many people and is focused on mild issues. Ask for DBT or IFS and EMDR for abuse, someone more trained - make sure she or you mention the history of abuse and bereavement at the GP so it will be on the form. Also you can self-refer to local IAPT talking therapies so try and do it for the trust she'll be in at uni, just search up the location, find the NHS trust and then search x IAPT self-refer talking therapies(maybe after results day and close to her moving in in a month and a bit).
Hopefully a GP at a surgery near her university (try and look for someone with mental health interest) can explain why ADHD medication can be so useful especially during university so she doesn't fall behind and can do really well. Hopefully they can also get her on medication might not be antidepressants maybe antianxiety meds. But even if she just takes ADHD meds those can have a massive impact along with therapy.
Also on her student finance account (she should have applied for loans by now) she can also start the process to apply for DSA. DSA doesn't count towards the money you pay back and they give you assistative technology (note-taking etc, lots of useful stuff). She will again need evidence from GP but doesn't need the full diagnosis most of the time. She'll have an assessment once accepted, but the needs assessment is not a test, it's just to see what support they'll give her. If she gets to that stage they've already accepted her application. Hope this helps, just try and be as supportive as you can, which it sounds like you are.
Also what is she planning to study at uni? Try and get her excited about that, and the fact that if she gets help, university can be such a fun time. Try and get her to think about societies she could join. It helps having something to look forward to.