Last friday I spent a good portion of the night hanging out with this girl i mutually met through friends and with her younger sister and also her friend. I had a lot a fun kino escalating with her she def felt me up

it was nicee. But then her younger sister got into a full out brawl with the girls roommates, it was was insane, i was the only male in the room when it all went down so i had to jump and stop then from killing each other. Anyways later that night i messaged her and told her that i was sorry that she had such a crappy night blah blah, and she replied telling me how it meant a lot to her that i sent her the message. So the next day i responded to her message blah blah and in her response she gave me her phone number and told that her sister wanted me to come and have dinner with the three of them. I got that message too late so i texted her saying sorry i couldn't come, you guys hanging out the next day? She responded that her sister had already left and thanked me for texting "us". So tonight i get up on my facebook and i noticed that her relationship status has changed to in a relationship.
I'm not really sure if its legit or if its because she's trying to send me a message saying don't try to date me. I did flirt with her sister that night a lot, so im not sure if she did that just so i wouldn't ask her out because her sister likes me more?