Congratulstions on your pregnancy.
It must be frustrating having MIL muscle in on your first baby. I was very lucky mine was, and is, fabulous.
I think you need to try and train her now. Yrs, it is not really your job, but it could make things better.
You could just ignore her comments, just smile when she says names, or you could say you don't like them and why (which sounds exhausting).
But in yoir shoes I would just say something like 'Choosong the name of our baby with dh is something I've looked forward to for a long time. It's going to be our choice and we won't be following anyone else's leads because it is so personal.'
Or you can think up another choice for hpw to deal with it.
When she offers advice, you don't need to take it.
You don't need to bend to any pressure.
If, for example, she wanted to be present at the birth, or visit you straight after or whatever; you can just say no.
You do not need to give a reason.
And if you do give a reason just go broken record "it's a special time for me and dh." Etc.
She can only muscle in and be overbearing if you and your dh allow her to be.