So, just to set this up for easy explaining, there are three of us in a throuple together: Lexi, myself, and the partner in topic, Karen.

K is 25, and idk what to say other than that i think she's losing her mind. L and I went on a vacation for a week and during that time we were gone everything kinda changed. Every day since we've been back its like non stop things that are wrong and have changed about her. We get back and she claims that she hit her head really hard while we were gone and ever since then she can remember everything that has happened since she was about 4 years old. She decided she was going to start a youtube career and has gone out and purchased multi thousands of dollars worth of equipment for it on credit cards. Then she came to us crying one day cause she realized she has adhd, too. (L also has adhd that she struggles with on occasion and is on adderall for.) In the next couple days it was that she's OCD. Now, shes saying shes starting to go deaf, but then always complains that everything is too loud, and that she is colorblind/blind, but everything is too bright for her. She has this green pair of sunglasses she almost always wears because the tint "helps her see better" but at the same time she's broken down and cried because "everything being green is overwhelming"

She backs all of this behind "not letting anxiety rule her life anymore" but says she's always anxious. She says stuff like shes "only going to do stuff she wants now and not do stuff because her anxiety"... but she went to the store and didn't put groceries away for three days due to "not wanting to due it because her anxiety is telling her to" so needless to say everything that was perishable had spoiled by the time we had gotten to it. It is really hard because some of the stuff she says she has the right concept but she's doing it all wrong in application and I just dont know how to make her see it. 

To L and I, this just seems like a giant beg for attention, but every time we try to give advice or try to help her in a way that doesn't follow her narrative we just get shutdown by her telling us "that's just your anxiety speaking" or "you're being destructive and triggering my anxiety." She's been caught up in lies with us in the past and anytime anyone suggests she's a liar she gets really upset.

K is in therapy, but she avoids the real problems and lies to the therapist. K's always misinterpreting whatever he says so that it fits into her own narrative and then holds it over L and I who also have our own depression and mental issues and acts very holier than thou as if she doesn't have the same issues.

TL;DR
Can you give us any r/advice? We really want to help her get on the right path, but we are completely lost on what to do. She's always been kinda controlling, attention needy, and kinda hyperbolic, but ever since she hit her head things have gotten 10x worse and it's become toxic. Her parents have suggested we take her to a mental hospital but we want that as a last resort. Therapy and talking to her hasn't really worked out too well and we are running out of options.