WIBTA for kicking out my emotionally and intellectually disabled sister who has nowhere to go

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The original was posted on /r/AmItheAsshole by /u/Obvious_Promise_3483 on 2023-09-18 23:04:23.

I (f26) was born healthy and my twin "Amy" was born with a disability; that birth guilt really set the tone for our relationship. Our parents sucked, so I spent our childhood trying to protect us both, mostly failing. We only had each other, which because of her limitations and volatility meant Amy only had me to rely on and I had no one.

I've walked on eggshells our whole lives to avoid setting Amy off and always given into her demands to keep her happy. If I had something, it became hers; if she couldn't have it (e.g., friends, boyfriends), I couldn't either or she'd throw a fit.

As an adult she has gotten more subtle: rather than just demanding things, she will complain to make me guilty and then ask for something (usually money). I didn't notice the pattern of manipulation until my fiancé "Brian" (m30) pointed it out, because this is how it has always been.

Amy isn't too disabled to work, but she can't delay gratification. As soon as she gets her paycheck she spends it all on weed, anime stuff, clothes, and makeup.

She was evicted six months ago for non-payment of rent and got fired around the same time for reasons I still don't know. She had nowhere else to turn.

I took Amy in, telling Brian that this would only be until Amy got another job. Now, Amy has a job but is still here. She's not helping with rent, paying for her own groceries, gas, or anything else but always comes home with new shopping bags. On top of Amy overstaying her welcome, Brian has become uncomfortable because of how Amy treats me (constant insults, guilt trips, and much more). Amy doesn't treat anyone else like that, but knows she can get away with mistreating me (at least when Brian isn't there.)

Last week when I found out that Amy has been stealing money from me the whole time she's been staying with us (she admitted it when Brian and I confronted her, but offered no apologies--instead making it all my fault). Amy spent over $2000 of my money that she stole, and that's on top of the hundreds I've been paying (without getting so much as a "thank you") to keep her fed, clothed, etc.

On top of that, the next time I came home from work before Brian, Amy cornered me and said she isn't coming to our engagement party because 1) she feels like I "only care about" Brian now and not her because I've been spending so much time with him and 2) she can't afford anything to wear to the party because I told her she needs to start paying for her own groceries and contributing to rent (before the theft revelation). It was Amy's way of asking me to buy her an expensive dress to wear to the engagement party and punishing me for setting boundaries.

If I kick Amy out she will have nowhere to go. When I first told her she had to pay for her own groceries she said "I guess I'll starve" and part of me fears she will. But, my enabling Amy isn't fair to Brian either.

WIBTA if I told Amy that she has 1 month to either pay me back the $2000+ she stole and pay 1/3 of the rent or leave?