Guess what money is tight, it's always going to "tight", just go do it.
She's going to wedding, I'm assuming that means she's going to make herself look presentable, bring a gift/presentation, etc.
That costs money, but money is "tight" ;-)
As for her comment, agree with her next time (it's too late now), don't tell her that's "your opinion!", that doesn't work.
just say "yeah you're right, I probably did do that quite a bit before", don't defend yourself when she says you do a certain thing or have done a certain thing, when you defend yourself against these complaints, you just invite more attacks like this, just get used to agreeing. You can either stand in front of that attack and defend yourself and prolong the fight or just let it slide off your back with less effort.
Don't get into the habit of watching the kids for her all the time as her "babysitter", if you have plans to be with the kids and it works out for you to take the kids when she's going out, great but don't let her get used to that. Good call on doing the same thing with her.
As for the "look" on her face, let her have any f!@#$king look she wants to have, LOL!
