It "could" be one of 3 things.
Either you've gotten the date wrong.
You could have mis-identified the ovulation. You could have thought the pre-ov swell was the actual ovualtion. If this happened you need to count 105 days from her last shed.
She could have re-absorbed.
I don't know if this actually happens. I've heard of boas re-absorbing the ova, but I've never actually seen it happen. She did look pretty big in the last photos, but in the more recent ones she doesn't look pregnant.
She could have had a false pregnancy.
Some boas go through the motions. I've seen females that have never been with a male "look" pregnant. These females go off feed, swell, stop shedding, and look pregnant, but never thin out in the upper body.
Pregnant boas almost always thin out in the upper part of their body "before" the thining out in the lower half. It's sort of like they loose weight, but not in the area they're carrying the babies in. Then a week or so before giving birth they thin out a bit in the lower half. This could be from the babies absorbing the yolks.
It's hard to tell from your recent pictures, but she doesn't really look pregnant anymore. At least, not from that angle. She could still be pregnant, but it's really hard to tell unless you have an "overhead" picture.
