I never met my grandma, who my mom says lives in a hovel and wants her to move in with us. Then I saw that word in Frankenstein. What's a hovel? I thought it was like a place that had room service.

You're thinking about a hotel, which is quite the opposite of a hovel. A hovel is a small shed for sheltering animals or storing supplies. It can also mean a really small, run-down place, like a hut, where people live with the barest necessities.

In Frankenstein, the "monster" is chased away by a bunch of frightened villagers, and he ends up hiding in a hovel:

The whole village was roused; some fled, some attacked me, until, grievously bruised by stones and many other kinds of missile weapons, I escaped to the open country and fearfully took refuge in a low hovel, quite bare, and making a wretched appearance after the palaces I had beheld in the village.