No to Plan B. It's not meant to be taken as a form of birth control. It is an EMERGENCY contraceptive. It contains a VERY LARGE dose of hormones. If she is going to be sexually active she should get on a daily birth control OR you should be using a condom.
Can she be pregnant, yes. Not from the 30th yet though, it's to early.
But, one of the side effects of Plan B is that her next few periods can be EARLY or late, and HEAVIER or lighter than normal. She has common side effects of using Plan B.
She should take a home pregnancy test at least 2, preferably 3, weeks after having sex. Testing now will let you know if she got pregnant back on the 13th. You'll still need to wait to test about the 30th.