Do I need a legal contract for mom to pay me for elderly care and expense like rent?

Here is a link from another page, addressing your question. Read all of the answers. One of them was from PA. If you think she will someday need to qualify for Medicaid, by all means, follow the rules. From what I have read at IRS.gov, the pay you receive for caring for her is not taxable (you're providing a service at a greatly reduced rate from a nursing home/rehab) but must be reported.

It's a good idea anyway, but strictly speaking you'd need a contract only if she wishes to pay you for your time spent caregiving. Her household expenses - a fair share of utilities bills, local taxes, groceries, plus her own normal outgoings such as toiletries and what have you - you don't need a contract for as such, but you must keep very clear records and documents of what she is paying; and her income and her own money must be kept separate from yours. You will also want to look at hiring care in to give you support (and time off occasionally) and it is perfectly in order for your mother to pay for that - it is her care she's paying for, after all.

More to the point, has she given you Power of Attorney? If not, and she is able to do that, then your best plan would be to see a lawyer with good experience of elder care and get everything sorted at the same time.

Well done to mother for volunteering! It's often a sad surprise that people living with their families think it somehow doesn't cost money to keep them :/

Currently there is a thread running where the poster is being required to pay back money the mother gave her/him as a gift - for the down payment on a house. 

The assumption is that the mothers finances are being given the five year look-back to qualify for Medicaid.

Least this happen to you, it would be wise to put everything into a contract drawn up by an elder care attorney. While food and rent might not be required to be in the contract - if it were me, I'd want to cover every base.

Better to be safe than sorry, don't you think?