I would suggest having a behaviorist come to the house and work on the problems they are dealing with. She doesnt "know she is bad"- taking things and darting off with them is a fun game for dogs- my Chloe still does it some times- but they need to work on a "drop it" command for those instances. She just sounds untrained- not "bad". I don't know much about maltese but I grew up with toy poodles and they are SUPER SMART- very very good dogs- the problem with very smart breeds is that when they are bored, they create their own fun which usually equals trouble. If your parents work on really training her with the help of a professional, she will likely pick up on things very quickly and be a great dog.
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