Easiest explaination is that she's not a tremper albino... but...
Maybe one of her parents was Tremper albino and the other was het for tremper (but both were secretly also het for bell or las vegas albino). She could have turned out to be a las vegas or bell albino but because one of the parents was a known tremper albino they just assumed she was also a tremper albino.
Strange things can happen though the odds get smaller with the more remote explainations. Perhaps if she continues laying you'll be able to get tremper albino young (if she's het for tremper). You're sure your other albinos are tremper?
Also, chocolates are by definition created from low incubation temps.
She looks awesome BTW... 