Riruka,tried to protect Tshukishima's well being.If she didn't moved out from Rukia,Tshukishima might have killed Rukia,because she tried to protect Ichigo.Riruka knew,that the attack is aiming to kill Ichigo,if it happens,Tshukishima might regret doing it,later on.Riruka does that,because she understands Tshukishima's feelings for Ginjou (not Rukia's nor Ichigo's),since she felt the same towards him as well,that's why,she can empathize with him.To Riruka and Tshukishima,Ginjou is the one who saved them.
Anyways,I might be wrong as well,but we will definitely see the answers to your confusions,when the next chapters was released ^.^