Why should Keiko have to come up with an optional field trip? We don't in this day and age ask science teachers to come up with optional field trips to church...that I know of, anyhow. If you want your kids to receive education beyond what they'll learn in school, you have the option of arranging it as a parent.
That said, I'll be the first to agree she didn't handle the situation as diplomatically as she might have. But then, she's not a diplomat, she's a botanist who decided to try her hand at teaching (I do wonder what her credentials were).
As far as being a "military spouse", it's not impossible to think that she thought she knew what she was getting into at the time, but DS9 was above and beyond what she anticipated at the time. I could see it being a situation where other spouses of Starfleet officers put up even more of a protest ("I knew I might get bumped around Federation holdings, but this isn't even Federation...it's practically Cardassian!").
I think it's a bit ludicrous that people accuse Keiko of being a "god-awful, horrible bitch" while failing to cite even one specific instance in which she behaved in that manner. O'Brien, of course, was a Saint.