Thanks for your question. If I understand well, when you put your finger in the vagina of your girlfriend, she was wet and you are wondering what that is.
The vagina naturally produces a liquid meant to reduce friction during sexual intercourse. When a person with a vagina is sexually aroused, they can produce a certain quantity of that liquid. The quantity varies from a person to another. It can also vary in texture, color and odor. It is totally natural that if your girlfriend was excited by your movements, she produced a little bit of vaginal lubrification.
Furthermore, some people with vaginas can ejaculate a clear fluid from the urethra during orgasm. That type of ejaculation is mostly accomplished by stimulation of the G-spot but, more rarely, ejaculation can be accomplished through external stimulation of the clitoris. This fluid is not urine and the quantity can vary from several drops to a few millilitres.
Hoping this helps,
François and Sabrina, for AlterHeros