Sounds like my last gf. But mine was doing alot more than just flirting. She just turned 20, im 28 and we lasted a year.

Does your girl allow you access to her friends? Like letting them talk to you and vice versa? Perhaps you could ask them what kind of girl she is. My girl would NEVER let me near hers in any way, which was a red flag to me. I dont know about youre position but in my case, she was hiding so much from me. I did get ahold of one her friends and turns out i was not the only guy she was seeing and cheated on me with one of them, possibly another. If you dont know if shes trustworthy, you need to either talk to her or her friends. If not it will just eat away at you.

From what ive read i dont see much to be too concerned with just yet as the info given didnt tell me much. Your girl may just like to socialize with the opposite sex. I do. It doesnt always mean something is going on back stage. Slapping a guys ass on the second day you two went out (6 months ago) i wouldnt be worried about at all. Exchanging pics i wouldnt be worried about as you say that was long ago to. Id say talk to her, nicely. Its always good to touch base every now and again. Communicate.