Okay, Strummer obviously thinks she is in charge, not your mom-in-law. It would be a very good idea for her to take Strummer to a basic obedience class, and it would not only help Strummer, but help your mum-in-law, too. Let the instructor know Strummer has issues with small dogs, and a good teacher can help your mum-in-law work on how to react in these situations. Strummer thinks she is the Alpha in the house, and obviously, right now she is. A good class will help correct that, and it can be fun for both dog and human!