Guardianship of Adult (my mother)

Here is my situation. I am 25, my brother 22. Our father recently passed away leaving a fairly large estate to our mother. Our mother is in a mental institution for a mental illness (in the State of Maine). Her assets (house, bank accounts) are in the State of New York. My Aunt (mother's sister who lives in New York) wants to become guardian/conservator of our mother and oversee her care and assets. My question is, how much control does the guardian/conservator have over these assets? Can the Aunt spend them on whatever she likes? Is there anything in place to prevent her from misusing these assets? Will my brother and I be able to oversee what she is doing with these assets? Also, until she becomes guardian (this takes 60-90 days) she wants us to pay for the mortgage, house repairs, bills, etc. I know it can be reimbursed, but I really do not feel confortable spending a large amount of my savings on some else's stuff when the economy is bad and I could lose my job. What is the best way to get these expenses paid before my Aunt becomes guardian (she claims that she can not afford these expenses)? Any help with these issues would be greatly appreciated.

You didn't say why you or your brother are not taking gaurdianship. The natural progression of gaudianship would go to one of you. If niether of you want this responsibility then whoever is designated as conservater will have final say regarding your mothers asset. I also understand that the conservater can be paid from the estate for serving in that capacity.
Who placed her in the institution? Was it voluntary or was she comitted by court order.
Your other questions will be answered in court depending on how the documents read.
If your mother is institutionalized voluntarilly she can give gaudianship to whom ever she wishes.