With my children any change in their home even somebody just sleeping over will cause a meltdown. If you dont want to co sleep ( which I highly recomend) then you will just have to indulge her and take the time to make her feel comfortable enough to fall asleep. she is most likely feeling insecure for some reason and its your responsibility to help her overcome that. Try a sleeping ritual that you dont ever break from. Its hard but it wont last forever. Good Luck.