They could have a story regarding their kids dealing with the gremlins maybe? If they do come out with part 3 I hope they stick to the roots of the movie. Brand new makeovers of classic movies never really do well - the nostalgia is what gives the movie a buzz.

I saw she did a Q&A for a screening in NYC with Zach Galligan and Dick Miller in 2015. So at least she hasn't run away from the property entirely.
Zach did say in a Q&A this month that his gut feeling is she would NOT do it, but he didn't sound very sure.
From the way Chris Columbus emphasizes that the story is going in a completely new direction in Gremlins 3, it sounds like there may not be parts for either of them. I don't know how you have Zach and Phoebe raising up little Gizmo (who himself would've aged 25 years since Gremlins 2, so I wonder how that will look) and still take the story in a completely new direction. That's basically what they were doing in Gremlins 2 already.
Colonel Miles Quaritch is like some sort ofnongiving-uparmy guy!