Are flirty girls bad girlfriends?

I am dating this girl, not officially but we have been on 6 dates and everything seemed great and all, we went on 5 dates and they were all great. Then she went on vacation and so i didn't think that would be so bad, well it kinda made things bad. There were alotttt of pictures with her and another guy and they were all over each other and they were both drunk but they never were kissing, well at least in the pictures they weren't. So i really can never know what happened when the camera wasn't around, well she explained that they were all just friends and nothing ever happened. (She told me this without me asking her) Well we went on a sixth date and it just seemed slow, she was kinda sick and i wasn't feeling well, maybe it was only me feeling distant or both of us, but everything felt different. We had another great date, it was fun and i really do still like her but i know with any other girl i would've been more open but for some reason i felt distant and honestly afraid because she has a reputation of being a flirt and plus what she did on vacation. So i guess i just am holding myself back now because i don't want to get hurt? Is this normal? Any advice would be great.