How can I finger my girlfriend if it hurts without going in?

Basically, I've been trying to finger my girlfriend, but everytime I get to the, hole, she says it hurts, I know its not because she dosent want me too, cause she deffinatly does, I'm thinking that she still has her hymn but she gets her period, obviously, but she dosent use tampons, soo help me out? Because I really want to finger her and eventually have with her, tips?