I don't know. When I started playing violin, I got a half decent one. It plays fine, but it's not a beautiful instrument. It's certainly a step up from what Grandma found, but you get the point. It was fine for learning fingering and bowing and basics.
Then, my DF got me a beautiful violin for Christmas. I was involved in picking it out, so no surprise. But, I love that violin. I play it every chance I get. It is my first love on the violin.
I still have the other one though. I can take it when I travel, or when I want to let a child play. Children love the idea of playing, but I'm not letting them touch my nice one until they can show me they know how to handle it appropriately.
I think Grandma overstepped. But I don't think it would occur to me that getting a guitar would need to be cleared through parents. I can understand the noise issue, but as for them giving it up, well, they give up most presents eventually. And the noise issue would depend on the living situation. So, if the dynamic wasn't already toxic, I would chalk this up to a misstep. With the background, I can understand why the OP isn't likely to do that, but I wanted to give that perspective.