What tax forms need to be filed since Grandma isn't being charged rent?

I'm asking this for my parents. Grandma has lived with them for over a year and receives over $10,000 a year in retirement. However, my parents are currently not charging her rent. They are only charging her for her groceries (they keep a list) and the electricity she uses (they compared the kilowatt hours used from before and after she moved in and charge her the difference). Grandma gives them $350 every month and any money leftover just kind of rolls over (my parents don't pocket it even though it does go in their bank account). Anyway, is giving them that money for her groceries and utilities something that needs to be reported on their taxes? Since she is just reimbursing them (they used their credit cards to buy her groceries) they can't see why they should have to report it. Also, since Grandma does not pay rent, I keep reading things about how my parents could possibly claim her as a dependent even though her gross income was over $4,050 for 2017. I also saw how they should/need to give her a 1099 form with the fair market value of rent listed and that it's considered taxable income to my parents. My Grandma's POA wants to file her taxes ASAP since she (the POA) is going on vacation soon. My parents aren't ready to file their taxes so they can't discuss this with their tax person yet. My parents are agitated over this because they receive tax relief and they're not sure how or if Grandma's income and taxes might screw that up. They need the tax relief discount. So if Grandma's income or taxes screw it up, they would need her to cover the amount of that loss. Basically, they need to make sure they aren't losing money because she lives with them and if they are losing money, she needs to cover that amount. The POA doesn't have a problem with that. The problem is what forms need to be filed.