Is it too late for me to draw up a caregiver agreement?

I need advice on a caregiver agreement. I've been taking care of my sister since February 2016 with no written agreement. Didn't know they existed, actually, until I found this website! I'm the only caregiver there is, and she's in hospice care. We live together, so I just sort of became the caregiver for want of any alternative. I have the POA. She is paying me $2,500 a month for my duties, for which I write myself a check from her account. (She put me on the accounts in February. She's unable to handle any finances.) No other family members are involved; there's one other sibling who is unwilling to help with her care. My sister has no children.

Is it too late for me to draw up a caregiver agreement? She cannot leave the house, so we'd both sign it and I could get my signature notarized, and/or we could get two adults (the long-term housekeepers) to witness both signatures. She has some savings, but I'd hate to pay an attorney when it seems like I could draw up a simple form. No other assets to worry about, just her savings. I would put in the agreement that this has been the procedure since March 2016, although it wouldn't be signed and notarized until October 2016.

I know her savings will eventually need to be used for a board and care home, as I won't be able to handle this alone much longer. I worry about the California Medi-Cal look-back, once her savings run out. I would hope she'd qualify for Medi-Cal to pay for future care, if needed.

I'd appreciate any advice. Thank you.