Is it normal for a grandmother to want to have her 7 yo granddaughter spend a week with her without mom/dad?

My mom lives about 100 miles from us. She has been asking to have my daughter visit and spend several days (and nights) with since she was potty trained. My husband is very uncomfortable with the idea mostly because he doesn't entirely trust my stepfather. I just don't want to leave her anywhere for several overnights. My mom is acting like we are being selfish jerks.