The only ID provided at closing was my grandmothers voter registration card which the notary accepted. Is this legal?

The voter I.D card has her photo, but it clearly states on the card
(for voting purposes only) the I.D card does not have all the elements that a driver's license has.

So far, every notary in Illinois and Michigan that my mother has been to has required a photo ID except for one notary that happens to know her, directly. But each state is different.

With that in-mind, here are a couple of resources that might help you. I just did an internet search for this and do not happen to know what information is in them:
http://www.nationalnotary.org/knowledge-center/tips-tutorials/determine-if-id-is-acceptable
natynotary/notary_answers.html

As a notary, I would accept that if she could correctly draw the signature and the address is the same. If there is no signature, sorry.

One would think a person would need a photo ID for closing for a sale of a home. My parents kept their driver's licenses even though they aren't current for driving [they stopped driving years ago], as the address is the same, and the photo still resembles them.