IMO, you need not feel bad about it bcos since she agree to only tc of your child then she shld stick by it.
how is the search of the other nanny gg on?
n for the other baby, is the job already on hand to take anytime or she just have an idea of doing so?
n will she charge you the same?if not tell her you wanna cut the price into 1/2, since she will only give your child 1/2 the attention..? (just test her.)
since you feel she is not a suitable nanny for you, i would suggest try to find another nanny asap. in the meantime, if possible, get a relative to help you tc of your child.