Lab Rats: Leo's Lost Half Sister

Long ago Leo had a big sister she ran away when she was 5. Leo grew up not remembering his sister that well. But she knew them all cause she would watch from a distance only Chase knew she was there watching but he didn't know if it was real until one day when she saved him on Christmas giving him a letter for Leo and Tasha without him noticing and leaving as quick as she came only to find a place to hide out and go to Mission Creek where she meets her half brother again as well as Adam, Bree, and a very suspicious Chase. What will happen if he rats her out as being the girl who's been watching them? Will she escape? Or will she have to use what she had been hiding as the reason she left?