Please take the money. This is very much about boosting her self esteem and giving her confidence, I think it is a bit unkind to reject it. Have you ever considered that deep down she really wanted the nanny, but is being kind to you?It would boost her morale to feel she is doing something for you, helping you as it were . Much better than being beholden to you which will add to her feelings of inadequacy,
I think that you should think about something specific that you want and perhaps take her with you to choose it. When ever I bought a gift for my mother she would say, “oh you should not have spent your money on me. You have enough to do with it”. Just once it would a relief if she had behaved graciously.