I think i caught her in a lie about bulimia?

ALL ANWSERS ARE APPRICATED, THE BEST WILL BE PICKED, DONT DO ALL INFO CUZ I KNOW THAT ALREADY, DO ADVICE FROM THE HEART!!! Ok so i was at a going away party for my friend at my other friend's house. we were all in the pool after we were eating and my 1 friend went to the bathroom 2 other girls got out of the pool to "scare her" but came running back in b/c they said they herd her throwing up. i belived it b/c she alawyas says how much skinnier i am than her and how fat she is. when i asked her she was all No. who thiks this do u why ? who!? then later she got sad and said y do u tink that and sarah said she herd her and she was like but the water was running then she told us yea she was but it was b/c she felt sick. THEN she was sad and sat on the ground. i asked her about all of this and she said she didnt want us to think she was, i think she was trying it and got caught and wont do it. should i be more worried? what to do?