I'm starting to think this is actually a really interesting question. All of the answers so far have assumed that she stopped being interesting and became irritating. But what if she just stopped being interesting because you'd learned everything there was to learn about her, and the initial mystery and intrigue was gone? She hasn't become dull, or tiresome, or boring, as such; it's just that you have ceased to be an explorer of exciting new territory, and she is now a known quantity to you.
In this case you might be able to say "initially I found her interesting, but after a while she became over-familiar (and I grew bored)".