Can My GF Take Plan B After Being On The Pill For Only 4 Weeks?

Shes starting week 4 tomorrow, and we ran out of condoms last night. So I put it (not to get into to much detail) in and out of her a few times for probably no more than 30 seconds. Also, earlier that day I masturbated so not much was in me except for maybe a little pre-ejaculation. I pulled out, (I'm a HUGE worry wart) and told her to go get a Plan B and told her I'd split the cost with her. Also, if she takes this, how much will this affect her period? Like will she be late? heavy? spotty? early? Am I over re-acting to this? Thanks in Advance!