She's curious, as all children are. She knows she has arms, legs etc. that she can identify as just the same as what you and her dad have. But she's now found an area of herself she's realized is quite different from what you have and even more different from what your husband has and she's naturally fascinated.
It's time for some simple explanation that hers will eventually change to become like yours, but that boys are different there and it's very special so we don't show that bit to other people.