How many days do you have before she is due to kindle? I have a doe that had three litters underground but never in the snow. I did everything I could to steer her to other areas, short of caging her, so the last litter I waited until she kindled, checked on the kits every day and then moved them to a nest box after a couple days. It had started raining pretty good and flooding was an issue. I made Shure she knew where I loved her babies to and she was fine. I wouldn't worry about snow unless you know it's going to be so deep either you or the mama won't be able to access her kits to feed them or check on them. Or... I don't know for sure, but I would think if you put your rabbit in a shed far enough in advance that she has time to get used to the idea of not digging a nest tunnel in the ground, and then give her lots of hay and long nest box she might have them there successfully. Watch her for signs of stress and agitation. she may have killed her other litter if she thought there was a threat and the babies wouldn't survive, or they would attract predators. If she feels safe, it may be different this time? You'll want to check on them frequently and possibly even "shelve" the kits, which is the process of keeping them separate from mom and only bringing them to her twice a day for supervised feeding.