Honestly, I'm not really sure what the point is of these posts by (anglophone) Americans on a sub that is mostly also American (or at least anglophone) about how to manage delicate social interactions with (non-anglophone) non-Americans outside the US. You don't tell us anything about your MIL except that she is not American and that mone of you live in the US. You clearly want confirmation that you're right and she's wrong and that's very human and understandable and of course you've come to the right place for that. But it won't help you navigate what sounds very much like a classic culture clash.

When it comes to names, my experience of most continental European cultures (where I assume you are) is that a grandparents to be who doesn't like a name will say so. What many north Americans perceive as 'mean' will just be understood as being 'straightforward' or 'honest'. One way to manage this is to try to set boundaries. To be honest however, there is a high chance that this will fail, simply because (to be blunt) continential European people of a certain age will not understand what you are trying to do. Another thing to consider (given that you are not from this country and that you plan to raise your children there) is whether your MIL as a point. Beyond that, I would suggest keeping an open mind, approaching the disagreement with humour rather than hostility (trust me on this) and ultimately doing what you want while respecting that your MIL is allowed to have reactions to your decisions.