No she shouldnt shed again. MArkus Jayne's website is good but confusing at the same time, to me anyway. This hobby has a tendency to not go by the book, as it is wild animals that we are dealing with. They do their own thing. 28 days? Pfft I waited 40 and was ripping my hair out around day 33. I didnt know if I was waiting on an ovulation, or if she was gravid, or what. But now that I went through it, and based solely on my experience so far, if she shed two times within a month, that second shed is the pre lay/post ovulation shed and you missed the ovulation in between that first and second shed.
You could always palpate her, if you feel anything golf ball sized and up, and its solid, then youre definitely waiting on eggs. Regardless, get your bator warmed up...if youre one of the lucky ones and your snake goes off the 28 day rule, you only have a couple days left.
What was the pairing?