How long has she been sitting? They tend to take a few days to really settle on their nest, one of ours was switching nests the first two days, but settled back onto her's when she was moved. Now she is sitting properly and knows where her nest is. I've never had one move her eggs before though, could she be getting bullied in the shelter?
She may well remain there now, and as I said it can take a couple of days for them to really settle.