I think your skull squares are going to be small enough they won't be so gruesome. You're making a quilt you know the mom will love. It will be cute!
My nephew and his wife had their second baby girl SIX years ago here in Texas. They are more into the "skull thing". My daughters and I made her a baby quilt with pinks and browns that did indeed contain skulls. I worried how it would be received but to this date it is her favorite and she keeps it on her bed. Her much older sister loved it so much she wanted one too so we did pinks and blacks for her. Yes, my fabrics were from JoAnns.
Don't worry or listen to the negative. I'm not a real cat fan, but I don't get on and cut down ladies who make cute quilts with cats.