You could still stop her if you had MK egret out before she does it. Block the first beam, then sniper shot. If you sniper shot on reaction it will probably whiff. In fact, there's a decent gap between the first beam and the projectiles, so you might be able to do that without the egret if you time it right (this definitely needs testing.)
MK egret is definitely still good, but there are 2 things you need to keep in mind:
He isn't going to help you advance and actually hit peacock.
Peacock can still hit you.
Conversely, he's useful for:
Punishing the opponent, since if she commits to one of her specials while the egret is out you should be able to hit them with sniper or at least get some napalm tosses out.
Covering an assist that works at long range and eats her projectiles, like hornet bomber or battle butt. Not really relevant to a solo thread, but I threw it in anyway.
Just generally taking less chip damage, all of her really good chip damage moves can't hit you while he's out.