has seperation issues it's in the beginning and gets better the longer family is away. Regardless, you need to find someone who understands dogs better and can deal with whatever is going on so the dog can accept being left behind.
Your Mom getting upset certainly isn't helping either of them. You may want to consider a pet sitter that comes to your house and stays with the dog and keeps the familiar routine going. hard to find a competent one but if you do . . .