She can try for B visa interview waiver, since she has a recently expired B visa. Make sure she lists your info accurately on her DS-160 form. MRV fee is still $160, whether her interview is waived or not.
If she is approved for another B visa, it will depend on the CBP officer on her every entry to determine how long she can stay (or if she can stay at all). By default, the allowed duration of stay is 6 months, but I've seen reports here on VJ of people being allowed much shorter stays, like 2 weeks or 1 month.