Is she cheating ?

Mygirlfriend started a new job about a month ago 2 days after she started the job she started getting text from her supervisor who was sending her stuff that made her smile and laugh. she then started getting text from a guy as she explained without me questioning her that he was having a problem with his girlfriend and she's crazy she was only trying to help him to understand her however soon afterwards she was receiving texts from him and without me asking merely explained that it was an inside joke about his girlfriend.she got very angry when she found out that my phone was locked I gave her the code to my phone immediately and said I was charging it at work and some guy got it and went through it and was looking at pictures of my children and if she has the code she shouldn't be worried she can go through it anytime I have nothing to hide and I don't have anything to hide.after saying that she would never lock her phone and now never has locked her phone she decided one day she would lock her phone I didn't ask for the code she then said she was going on a hike on Saturday with four women she gave me the names she had never mentioned these women before and she only mentioned them the one time the day of the first hike she got her hair done and then went on the hike her phone she said was in a place where there was no phone service because I tried to reach her to see how her day was going she didn't get back to me for 4 hours on that day. the next Saturday she went on a hike for 6 hours she didn't get back to me it was a different place where she was hiking and apparently no phone service I asked her about the hike that everybody enjoy it and she said yes and did not elaborate on any experiences there this is unusual for her she likes talking about everything she goes through. On the third hike I texted her and said I hope you have a good day have fun out there she didn't get back to me for 8 hours and her phone did not work no answer out of service area apparently.the fourth time this happened I was out of town for 15 hours I could not reach her I was worried and didn't know what was going on she finally got back to me and said that she had a mental breakdown and was drinking at a casino until 3 she did not elaborate on which casino or whoshe did not elaborate on which casino or who she was with and I didn't ask. I she cheating ??