Well, it wasn't a war exactly.
After all, I was blessed with an MIL who knew her boundaries. But still, vacationing with her proved a struggle in its own way. She parents differently than I do, and her son and my son were caught in the crossfire lots of times. Thankfully, hubs was always on my side, since we talked about and continue to talk about how best to parent our child. And I managed the grace to pick my fights.
So my son ended up drinking a lot of juice (because i'd rather he drink water and eat fruits, not drink sweet drinks that are never really that healthy). And eating fruits before meals (and not eating much of his main meals). I also had to allow for more mess than usual, and tolerate more spills and stains on my son's clothes.
I still really enjoyed our vacation even with this particular stress. At least I can't fault my MIL for not being a doting grandma. And I know that there are worse kinds of MILs out there.