How much more to pay a nanny for another baby?

Rebecca

My husband and I both work and we are expecting our second child in November. How much more do you think we should pay our nanny for taking care of two kids instead of one? I asked her, and told her to think about it (I was trying not to put her on the spot) and she insisted that she did not need more money, that she loves working for us and cannot imagine working for anyone else. Regardless, I know she is going to be working harder when baby comes and I just want to make sure we stay competitive. Any recommendations?