What's said is said, but I don't understand why you think it would have hurt her feelings if you said you didn't feel the same. Sometimes it takes a nudge for people to even see someone in a romantic light.
In my opinion, I don't think you need to 'force' anything. If you are open to dating her, why not just go out on a few dates and see what progresses. When you're seeing her in this new light, you never know what could happen. She may decide after a few dates that she'd rather stay friends. I guess it ultimately comes down to what you want. If you are 100% sure she is just like a Sister and will never be anything more then you need to tell her that. If you're open, see where it takes you.