Definitely worth pursuing. Think you missed an opportunity with "bending over is hard" line. The fact that she liked the "stretch you out" line is a great sign. I'd go with "So judgey ;). We'll stick with the personal trainer/Client roles, but fair warning... I make my Clients sweat. Especially the bratty ones"

She's just teasing and testing you to see how you'll react. Don't be serious dude, just turn this into funny banter. Say "It's a sexy classic though. What's your fantasm?"