No, no, no. She shouldn't growl back. Your husband isn't helping.
Yes, yes, yes, fire her. Don't give her two weeks notice. You don't want a fired nanny taking care of your child. You don't want her in your house either.
If you want to be kind, you can give her a week's pay. It's according to how long she has been working for you. It sounds like she is rather new. If she has been working for you for less than 6 months, I wouldn't give a severence.
M., it's good that you understand your son's issues. I do hope that he is getting OT to help with his sensory problems. I also hope that the next nanny you get actually understands child development. This one that you have is not a nanny. She might be a MOM, but that doesn't mean that she is nanny material. A nanny has experience dealing with children and is able to help children work WITH them towards good behavior. They have a "bag of tricks" of tried and true methods to handle children. This woman doesn't. She evidently doesn't even know that there is nail polish remover in the room she has put him in. Someone SO ineffective as to not know how to unlock a locked room just has no business being in charge of your child. She acts like a babysitter. You aren't paying for babysitting.
It's not just discipline and authority that you want in your next candidate. It is an understanding of how to work with children, like your last lady had. With this understanding comes the knowledge of how to handle children and stand up to a 4 year old's antics. There has to be strictness AND kindness and love shown to your child. Punishment isn't the answer. All this lady knew how to do was punish.
Actually, you are doing you both a favor by letting her go. She is in over her head and you hired the wrong person in the first place. Time to start over. I hope you have good candidates and that you hire a better person this time.
Good luck,
Dawn