L.N.
I would split the battle. Nix the candy but let the naps go. If it's only a 'now and then' basis, she won't do any harm by letting her stay up. Grandma's house is supposed to be a fun place. Give her a list of approved snacks (could be she just doesn't know that there are ok alternatives to candy) like fruit snacks, granola bars, etc. so she can feel like she is giving 'no-no' treats. That's what grandmas do sometimes and she likes to do it...don't take it away completely.
These are lessons I've learned after 3 kids. My mom sticks to my rules, but I don't ask her to refrain from being a 'spoiling grandma'!
~L.