Life Tenant on a Deed

My Brother, Sister and myself purchased a property for our Mother who is elderly. She is requesting to be a life tenant on the deed to help w/payment of the property taxes. My concern is that if she becomes incopasitated and can no longer live on her own in the property, are the 3 of us allowed to transfer the deed if she is still alive or does the deed now have exception and non transferable until the death of the life tenant?