Females like to speak most of the time. If she is not speaking there is a reason. Maybe it is something she feels she has to get through on her own. Explain to her you are there for her no matter what and she is not alone if she wants to talk about anything.
just act like you see her making a a weird like depressed or sad face and say "something bugging you?" if she says no just say "then y the face come on you can tell me anything" just keep prep talking her until she does
Then sit down a talk to her and tell her just what you told us. Yin makes a good point about girls liking to talk to express their like or love for a guy so maybe some more communication is in order. Communication is the biggest part of any relationship.