I put my finger on my grl frnd's vagina,just touched,might be precum on that finger,is it possible she get pregnent.she dont have period yet,?

Possibly: Most older studies have shown low levels of sperm or no sperm in pre-ejaculate with sperm not being motile (however, don't know how promptly samples were examined). However, a study published in 2011 showed that there are some individuals with a high motile sperm count in pre-ejaculate. See: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3564677/