6 year old half sister acts like she in love with me?

i know shes only 6 and we recently just met each othe like 9 months ago and she excited to have a big sister..but when she sleeps over my grandmas house she acts like she likes me shes always smacking my but, licking my face or acting like shes going to kiss me...then me and my aunt who i recently met also from that side gave me a wierd look because me and my half sister were taking pictures and she licked my face and my aunt saw the picture..so what do you think i should do??