I agree with all the others. It's high time Billie got a taste of freedom. Most WILL return to their cage on their own if given the time to do so.
Good to hear you've already started letting her come out and are doing it on her terms. She'll come out when she's good and ready.
Be sure to keet proof that room Lane. Windows and mirrors covered. Look for places she could possibly fall behind like bookshelves, dressers..entertainment centers..and take care of the problem spots beforehand. Close the door when she's out so she doesn't decide to take of to the rest of the house before you're ready for her to venture further.

Like Tess said, some/most don't fly well at first. They're not used to it of course. Expect a few crash n burns until she gets that pilot license. LOL IF she does crash n burn don't just go running to pick her up. Give her time to get reoriented and gather her thoughts and see where she goes from there.
Eventually a playgym to land on would be nice. And if she likes toys put some on top of her cage so she has something to do when she's out smile

Be sure to let us know when she finally ventures out.We'll be waiting to hear all about it.