How can you get to know your yaya better and bond with her? I think it's important to treat them not as a mere employee but a real person.

My uncle would always tell me that "pakikisama" is very important, so they will feel at home and would consider staying longer. We used to have a nanny, she has grown so comfortable that she would even treat us, our family, sometimes. During day offs, she would surprise us with a box of pizza or any snacks. My grandfather has always introduced her as his niece and she has been like a real family to us. I think that's the secret. They shouldn't be demeaned at all costs and should be treated like a family. But of course, it's a case-to-case basis. Be wary of those unscrupulous ones, though.