My GF is like that too, hardly ever dominant and it's so annoying. I'm fine being dominant but she hardly ever initiates sex. There are times when I want to feel wanted that way too, just because I'm a guy doesn't mean I always want to be in charge in those situations.
And I've tested it, if I just stop initiating we just don't have sex and eventually she'll get mad that I don't want her when at any moment she could just say let's fuck and I'd be all into it...