Here's a few stores that I try to hit when I am in the area. It's been a couple of years so I am not sure they are all still in business. Since fabric is so much more expensive in Canada and we have a cottage in eastern Ontario, I've never crossed the border at Niagara Falls to fabric hunt. I've heard there are some nice shops.
Pine Grove Quilt Shop, Delaware Ave, Buffalo
Quilt Farm, Colden
Favorite Fabrics (an online store that let's you visit if you call ahead), Orchard Park
Carriage Quilt Shop, East Aurora
Aurora Sewing Center, East Aurora
Marie's, Lockport
Sew What in Williamsville
Enjoy your trip and your visit with your sister!