If this girl likes me i would love to know. If not i'd love to be slapped. Please help?

seems as though there were a few subtle hints there to me. She had to notice you grabbing her hand, she acted as if she didnt because she obviously like it. I think she may like but doesnt want your sister to know, not yet anyway. Flirt with words next time and see what she says! Go for it dude, just dont be pushy.