Hmmm, these are tough questions.... especially with the threat of a growth spurt and the fact that you don't want to encourage snacking.
If it were me, I think I would feed around the same times that she normally would be fed. That way she is sticking to routine, but just getting some extra cals. I think, in essence, it's kinda like a cluster feed, but in the a.m. I would just encourage her to nurse as long as she can during the regular times.
I hope this helps.
But then again, she is your lo and you know best. I don't want to be responsible for her developing a bad habit. But I think that is what I would do myself.