Need Advice on pricing

My mother is a nanny in the North Dallas, TX area for a young married couple. Both of them are medical doctors and my mother has kept their 2 year old daughter for a year. They told my mother after 1 year she would get a raise although the amount was undisclosed. (Her 1 year mark is next month)

The mother is expecting a new baby in a couple of months and they have asked my mom to let them know what she feels a new hourly wage would be for adding a new infant. They also want her to start doing educational lessons with the 2 year old as well as help with some light housekeeping.

What would a fair hourly wage be in this scenario? She is currently making $19hr with a guarantee of 40 hours a week.

My advice was that: 1) She was already in line for a 1 year raise which she should get regardless of new responsibilities / added child 2) She will have a second child to care for that is an infant 3) She has additional duties with cleaning and educational lessons for the 2 year old. 4) The parents are buying a new house that could potentially create a longer commute for my mom.

Is $25 an hour reasonable or a low amount based on all these circumstances? Seems a little low to me for a high income family, in a high cost of living area (North Dallas) with 2 young children.