Great news that she was a nanny before being a teacher and that she has experience with new borns.
A pay rise does seem like the right thing to offer.. but as. you say, it is not at all costs. If she rejects your offer, then there is not much you can do. However, maybe it is another factor that is playing on her mind..
Nanny having a conversation in her own head.. MsKBee has told me she is having another baby, shit, does that mean that she will expect me to cut my hours while she is at home, how the hell will I pay the bills if she does, I hope she doesn't expect me to work part time for less money and then just pick up with an extra child when she goes back to work, the reason I gave up teaching was that I didn't like having loads of kids around, it will be mayhem with three, shit... what am I going to do, she is being really unreasonable if she expects me to cut my hours,
and then that gets blown out of proportion in her head, she assumes you are being unreasonable, she can't believe you have carried on every day, knowing that you are going to cut her hours and not telling her, because you are selfish and you don't value her as an employee, you are just going to hand her her notice and leave her up shits creek with 4 weeks to find a new job and only 2 weeks redundancy pay, she can see how much your eldest loves his nursery hours, maybe you will send the older two to nursery and stay home for a year with the baby and then get a cheaper nanny when you go back.. things are going to be tight with an extra child in the house, maybe you will give up work altogether, move to the country and get goats, I bet you got all this planned out and you don't want to tell her so she stays till the baby arrives.
And suddenly she is grumpy all the time... and as soon as you open your mouth she tells you she is looking for another job and will leave when the baby arrives and nothing you can do will stop her..
Can you tell I have been through this.. it hit me like a train and it didn't go well... I managed to convince her to stay when the baby arrived but somehow she had changed in her attitude towards me and it was really awkward when I was at home. We parted ways, mid maternity leave and I got a new nanny when I went back to work.