[souffle]

Some hamsters have a genetic disposition to doing this and once they have done it once their are much more likely to do it again and again. Unfortunately everytime they do it it causes stress on the organs as they are partially shutting down and the warming to bring them round again and the actual action of bringing them round impacts on the organs. It is likely the light - going from bright to gloomy or dark is confusing for them. Try keeping the room at a warm and even temperature and siting the cage so window light is reaching it. If this is tricky then you could use a daylight bulb and leave that on for 12hrs a day so try and keep her on an even light system. The vet won't be able to do anything to stop her doing this but they could do a health check and maybe test her urine for sugar?