Make sure your fridge is full of the essentials:
POTATOES, lots of them. Yukon or so=not red.
Dries mushrooms- no ladies, not for when you need a break, but for her to cook with
Sour cream- she will be happy to have something that resembles "smetana"- it's used on everything. Whether on blinys or Borsch- Sour cream is IMPORTANT.
Good loose leaf tea- Darjeeling or something. None of those pesky earl grey tea bag stuff- after all, that's just "leftovers from the factory".
Honey, nice golden honey. Always good for tea. Rasberry preserves to go along with it.
Or look up the ingredients for "borsch" (red beet soup with cabbage- different than the jewish New York Borsch)- and ask her to cook you some soup. I am sure your DH would love some too....
Some sourdough bread, basic cheese and butter. But again, depending on how old she is and where she comes from she might not be a babushka in house clothes and slippers but more fancy and modern than us...
Take her to the grocery store with, show her around, ask what groceries she would like and aside just repeat to yourself "it's just visit"...
And ditto on the "draft"= I know my mother would double over from a heart attack if she knew my son drinks something RIGHT OUT OF THE FRIDGE. Because that's how sore throats happen. Oh, if you run around after a shower with wet hair- be prepared for comments because that's also how you get sick.
Ditto to slippers, veeeery important- I remember being nagged to pieces about "house shoes". (my mom is Ukrainian)
Oh, ask her what she would like to do on "Pascha", and check on what date the "orthodox easter" falls. Maybe she would a "Pascha"- the italian "Pannetone" sold here is kind of in that direction. Close to fruit cake and gets eaten buttered and with tea. Maybe she'd like to hang some plastic eggs.