She has been in a nursing home for almost 5 years. She is well taken care of with insurance and other money my stepfather set up for her, she is good for many more years. I now have health issues. Am I able to access that checking account that I am the benificiary of? I share POA with my two sisters... thanks for your time and any help.
That money is your mother's money. You can no more use it than you could help yourself to any other person's money on the grounds that she doesn't need it and it's almost certainly coming to you eventually anyway.
I don't know if you have a range of other options, but this is only an idea - would your sisters be prepared to lend you money (of their own), using the funds in the checking account as a kind of informal, hypothetical security?
Especially for a POA it is illegal to dabble in any of this money held in your Mom's name. It is hers until death. You have a fiduciary responsibility to preserve all of her monies and it is against the law to start distributing funds to yourself. You are accountable to keep meticulous records of every cent spent for your mother, all receipts, and IRS filings and etc until her death. At that time the Executor takes over.
A beneficiary is a completely different thing, however. As others have said, a beneficiary only inherits the assets after the account owner's death.