If she leaves her real estate to me via Affidavit of Survivorship, am I able to just keep up her mortgage payments after she passes, or do most first lien mortgages have terms that prevent me from making her payments or something?
If the debtor dies owing a balance on a mortgage, the lender can call the note.
Most lenders don't call the note, as long as the note is current.
If the payments stop, trickle in, or get in arrears; lenders rarely will NOT hesitate to call the note.
What is call the note?
Definition. A callable loan gives the bank the right to demand immediate payment in full. ... Calling a loan can be a costly process for the bank, especially if it calls a loan you can't repay. Banks often exercise a call provision as a last resort due to a breach of terms.
https://www.avvo.com/legal-answers/can-the-bank-call-a-note---and-take-our-homes--503295.html
As with most things in life, YMMV.
Even if the bank ignores your granny's demise, allows you to pay the note, you pay the note off in full one day, owning the property can end up being an onerous task.
Unfortunately my credit won't allow for that.
If you have credit problems, paying the note on a mortgage is only part of the story when it comes to BUYING a home.
Notice, I type BUYING, rather than OWNING.
BUYING a home is just another form of debt, debt that most people never get out from under these days.
Based upon your evaluation of your credit, you might simply advise granny as gently as you can, NOT to involve you in her financial affairs because you can't afford to pay the note.