Yep most AAS will "interrupt" a period. Doesn't mean you can get all crazy and have free-for-all-no-baby sex. Another thought JFYI - if she's prone to yeast infections, she might want to include acidophilus or a product called "Fungal Defense" -- AAS, similar to some anti-biotics, will throw off the balance of "good" & "bad" bacteria "down there", and can result in a yeast infection or vaginitis - these usually require a trip to her OB/GYN for a round of anti-biotics to clear it up. Just somethign to be aware of.
If her period disappeared, it will usually return the month following the completion of her var cycle. If she's also made a significant change in bodyfat she may also experience a continued loss of period (e.g. for a competition) until her body settles in to a more regular schedule.