Homeowner passed away w/out a will

[Mark Paes]

I came across a lady whose mother passed away a few months ago. The house was in the name of the deceased.
The daughter, Lisa, lives at the house and handles the bills. The mortgage company deals with her. But she is not sure what is going to happen with the house. Her mother did not have a will.
She would like to sell the house, because she has a sister that wants to freeload on her and not help with the bills.
So, Lisa just wants to sell it.

My question is, what does happen if there was no will in place. The mortgage company treats her like the owner. Is is possible they were not informed that the name on the mortgage has passed away? Can Lisa legally sell the house now?

It is in Pennsylvania.

Thanks.