Get her Mom involved and find out why all of a sudden she doesnt want to leave her mom, something maybe upsetting her, have there been any new relationshipds in her moms life, change of home, school .If she still does'nt want to leave her Mom I dont think its a good idea to push her .good luck
This will be hard for her because shes used to being with her mum all the time, when i had my second child my other son was four, well things went wrong in labour so i was stuck in hospital for 5 days hes never spent a night without me and he cried for me all the time, have her mum have a word with her, you dont really want to take her if shes unsure,