See clip from Attorney Rajiv S. Khanna's conference call video that addresses this question.
If you go to this website - http://www.dol.gov/whd/fmla/ on Family and Medical Leave Act the website explains a lot to you that you can go 12 weeks easily and USCIS will honor that and they will still consider you to be in status. So even if you don’t get paid for that time and you don’t get a pay stub that’s fine. Now if there is a medical reason for eg: a pediatrician saying she needs to have x number of months of leave. I think she will be in status. We had a case were one of our friends had to be hospitalized for extended period of time and then she was out of work on H-1 for almost a year but we were able to convert her to H-4 because the government realized she was not out of work because she didn’t have a job it was because she had a medical necessity.
As for the question if she changes her status to H4, and file premium processing, she is not subject to the quota if she changes into H-4. But the employer will have to file H-1B change of status which is almost like doing a new H-1. Also COS from H-4 to H-1B be filed in premium processing can be done.