I'm not as experienced as I sound, that windowsill dormancy was only my second successful dormancy, but here's what I did. I kept my venus fly traps outside until it got down to really cold temperatures (somewhere below zero I think) after that I put them in some apothecary jars, though any glass container should do, and kept them there until it got warm and they started growing again. I too, suffered from a cold snap, but I brought one in that had divided a bunch of times to keep the little divisions from getting too cold. I thought the the others could handle it, I'm now hoping they make it through my mistake. I would suggest watching the weather report and bringing them to your windowsill until the cold snap passes. I hope that helps.