If you don't want to make them, then don't. You have no obligation to fulfill every request for a quilt, no matter who the asker is. I would tell your niece that have many projects going and know that you wouldn't be able to get to them in a timely manner. If she's miffed, that's her problem not yours. You could refer her to a LQS who might have names of quilters who are looking for business. She might not want the quilts made once she knows how much someone really would charge her.