Yes, you can file an I-539 twice to extend her stay further, but she should not remain in the US for more than 1 year, so you probably don't want...

Yes, I agree with these answers, she can apply for another extension. But if she does not apply for another extension for February, she should not...

Yes, that could be an issue at the border. I would recommend having a return trip planned and being able to show that future ticket at the border.

Adding to the answers above... In fact, you will need to prove that you intend to leave the United States after your stay on one of these visas is...