Is it possible get crabs (pubic lice) from someone who doesn't think she has them?

Difficult to answer. Well, if someone truly does not have crabs then that person cannot give crabs to someone else. However, if that person is not telling the truth and actually has crabs then certainly it can be spread to others.
Sure, She may say she doesn't think she has them, but indeed may have these little critters! if so, she can pass them onto you!

Related Questions

Do lots of people get pubic lice, or is it unusual?

Common. Particularly more common in younger people with more frequent sexual encounters with different people. Lice have been around for millenia, and will probably out survive humans. Read more...

Can I get pubic lice on my scalp?

Possibly. It is possible, but less likely, because of the texture and type of hair is different between the scalp and pubic region. Read more...