A shield might be possible
to justify, but it's not wanted. Maybe we need to better define what the limits of the gravity control are, because it sounds like it's opening a couple of cans of worms.
One of the problems with fictional technology of this kind is setting limits so that it's possible to tell stories in the way you want. Unfortunately, once you posit FTL flight there are just an enormous number of magical implications. This is a big reason that the uses to which technology is put in just about every space opera that goes on for any length of time - "Star Trek," "Star Wars" et al - are so remarkably inconsistent.