That just comes from being a loving mother, and I really don't think you have anything to worry about. Suddenly she has found herself responsible for this precious little life, and loving this child more than she has ever loved anyone, and that's a feeling that no one can imagine until it happens to them. She simply wants to reassure herself that, no matter what happens, her baby will always be safe, secure, and loved. I've been there myself - I had thoughts exactly like that - and I remember it very well.
She sounds like a lovely, caring and thoughful mum to me.