Traveling while crazy

Please forgive my use of "crazy', but I'm in a quandary.

Several weeks ago, I planned a weeklong vacation in California. Art exhibits, a great concert, staying by the beach. I was paying for my airfare, lodging and car rental, and I figured that for just the cost of her airfare, I could take my best friend along. Social Security is her only income and she was thrilled.

The thing is, she is very depressed. She lost her mother about a year ago after a long battle with dementia. She, along with her brother, were her mom's caregivers. It's been over a year now, and she's not getting better. She's actually getting worse. I have suggested she go into a hospital for a while, a place I've been to myself, but she refuses.

For a while, she has been hearing voices. She thinks people are living on her roof. I, gently, say "No, they aren't", but she is insistent. Her brother, who still lives with her, tends to get angry with her, so that's no help.

So we are supposed to leave for CA in 12 days. Normally I would just say that the trip will be good for her and lift her spirits, but these delusions are something I've never dealt with. Should I tell her she has to go in the hospital or I'm cancelling the trip? Should I just cancel no matter what? Or should I still take her and hope for the best? I struggle with depression too, and this stress is starting to affect me. To top it off, I start a new job on Monday.

Thanks!