Its not different then poeple capping lights when scars came out to go solo farm base feet. She over reacted, since its only exp and since you were even killing for exp. It would have ended no different then if your leader told her from the start. On top of it really 2 dds and a healer is enough to farm TEs and make great exp.
Have you joined many pickup xp groups? I'd say you are extremely lucky if 1-2 have any atmas at all, try what you just said with 2 DD and a mage with no atmas. Also it's kinda different for 1-2 people to do it than 1/3 of the alliance (some possibly on hard to rep jobs) and even worse to do it to a friend, basically making them replace your group that just bailed on them...this aside from the fact they pretty much did nothing for the xp alliance at all since once they capped lights they bailed. I would of at least stayed an hour or so to give something back to the people I leeched off.

This is no different than joining a pickup group for seals and bailing right after you get that 1 seal you needed, nevermind you are the only healer or on an important proc job. You can rep them but it's still rude and selfish and even worse to do it to a friend.