naw, no way they would've added a second weapon unless they were adding a weapon from another event, which is still unrealistic for their standards... but at least they've kept the usual event rewards... I hope that I can find a Rag at least, to do the event mission, if there is one...
I'd say MLB her, since you're a new player, and she'd give better stats than SRs [just don't give her any +1s]
you don't really lose out on anything, since you get the same amount of orbs for a MLB girl as you do for x5 0LB copies.
and later you can still get some Eidolons with future events AND the epic quests which will eventually give super good ones with nice summons/stats.
After the anniversary next year, leveling eidolons and weapons will be soooo much easier since you level with orbs instead of weapons that you need to make space and farm for. You get the orbs/weapons in thousands and they just stack up over time without having to worry about not having enough space for them.