In your shoes I would do what Misty suggests in option 2 - maybe adding in somehow about her trusting you to feed in whatever manner will cause least disruption to the day because you do understand it is her day.

What a truly awful situation to be put in - my DS is similar age and often will go a whole day without feeding but when he wants it, he wants it. Even if he didn't feed on that day it would make the whole thing feel uncomfortable to me - it would make me feel really uncomfortable being there (me feeling tense is a sure fire way to make him want a feed too).

I really think that it is very bridezilla - and is a case of her completely over-thinking it, but can't believe she has been prepared to put your relationship in jeopardy by asking it. Do you know if your BIL even knows about it?