Miffy,
During the interview with the maid, you can also ask her to do some simple housework and carry your baby or even let her feed her one meal, to see if she is good at handling housework and taking care of baby. You can see her technique only in doing some simple work so it is very important to ask her to 試工...
Also, do not fully trust what the maid's ex-employer said as they may sometimes bad mouth the maid or do not want to disclose information to you. In this case, you must trust your intuition towards the maid and the first impression is very important.