I don't know the signs of a liar. I am very confused and stressed. I don't know what else to do because I don't want to leave her. I just want to sort it out. I've tried serious chats and it just seems that I am getting lied to.
Female masturbation is a normal sexual practice.
It is perfectly possible that your girlfriend may like to masturbate AND also like having sex with you. Unless I'm missing something important, I think you being stressed out by the possibility that she masturbates is YOUR hang-up and not anything she might be doing wrong. It doesn't have to be that way. Let it go. It does seem that you don't trust your girlfriend.