yes you can. It's less likely than if a man ejaculates in her vagina but there's still a chance that the sperm could make their way into the body.
When did this happen?

is it that possible to get pregnant? how likely or unlikely is it?

Yes, its possible for her to get pregnant when sperm comes in contact with the outside of her vagina even when there is no penetration.

There's no set percentage, its just possible.

If this happened within the last 120 hours (5 days) then she can take Plan B in an attempt to prevent any possible pregnancy. Next time, use condoms if there's ever a chance sperm could come in contact with your partner's vagina-- it saves a lot of worry.

whats plan B ??

Plan B is emergency birth control.

Why are teens "humping"? Clearly, if you don't know the potential risks of your actions, you shouldn't proceed. As far as Plan B is concerned, it is not a birth control type tool to be used by teens. Instead of Plan B, why not try abstaining - that means no "humping" or "bumping". That way, you won't have to worry nor will you have to abort an unwanted child via Plan B.

Plan B does not abort anything and has no effect on an existing pregnancy. And it is a "birth control type tool" that can be used by anyone-- including teens. Only because of its low effective rate and rough side effects should it be avoided for regular use.

Important Safety Information:

Plan B® isn't effective if you're already pregnant, and it won't terminate an existing pregnancy. Plan B® doesn't protect against HIV and other sexually transmitted diseases (STDs). Side effects may include nausea, abdominal pain, fatigue, headache, changes in your period, dizziness, and breast tenderness. If your period is more than a week late, you may be pregnant. If you have severe abdominal pain, you may have an ectopic pregnancy, and should get immediate medical help. Please see important product information on adjacent page.
http://www.go2planb.com/index.aspx

Please do not promote false information here. Plan B is not an abortive medication. Abstaning does not always work. That is why I am a HUGE advocate in safe sex practices, such as birth control, IUD's, Condoms (ALWAYS, including "dry humping",etc), STD prevention and maintenance, STD symptoms/diagnoses...all of that. Because simply telling your teen "no, that is for grown up's" does not always work. This forum is proof of that. C'mon...raise your hand past teens....how many of you thought you were "grown up" at 16, no matter what dear mommy or daddy said?
In fact, if you read a lot of the threads, it seems most of the girls on here are grossly misinformed about sex due to the lack of education from their parents or from abstinence-only education, either that or they were sleeping during sex ed class lol. But seriously, how many of you girls think you were actually taught enough? How many are here for failed birth control/condom breakage? It just goes to show that either you didn't know enough or that you tried your damndest to avoid pregnancy and it occured anyway. That is life. Nothing is foolproof or predictable. Not even abstaining.