Hi there and thanks for your question. This can be normal, but sometimes it's not.

It's important to rule out the possibility of there being something wrong, so it would be a good idea for your girlfriend to see her doctor just to make sure that everything is okay. Then she can relax and stop worrying.

If she has been sexually active then there is always the risk of a sexually transmissible infection (STI). While STIs often have no symptoms, if there are symptoms, one of them can be bleeding after sex (including fingering sometimes). So if there is a risk of this, you should both have a test for STIs. She can talk to her regular doctor about this or go to a Planned Parenthood clinic if there is one nearby.

Another cause of abnormal vaginal bleeding is abnormalities of the cervix (the neck of the uterus or womb). However if she is young this is quite unlikely. The way that these abnormalities are picked up is through Pap tests (simple tests that can help find changes in the cervix that could lead to cancer if left untreated). In the USA, Pap tests are recommended once every year, beginning about 3 years after a woman starts to have penetrative (penis in vagina) sex and from no later than 21 years old.

When she sees her doctor it would be a good time for her to talk about contraception too, if you are thinking of starting to have penetrative sex sometime in soon. All the best and take care.