I don't get why she would not seek help either. However, one thing I have learned from sleuthing is that something that is totally illogical to us, is perfectly normal or tolerable to another. I think we forget how young she was. In her mind, she had at least one friend who knew she was lost, and she probably thought she had her back so that was enough. I can see how she just wandered; I think we see her just as it is dawning on her that she doesn't know where the heck she is at McGrady's. She doesn't seem familiar with that place at all IMO.
As for GPS, I never seem to get consistent results and that is when I am lucid on a good day. Those apps are highly idiosyncratic and tricky to master IMO. I think she was probably too inebriated to even attempt it. What I don't get is why she would not ask directions using SIRI? Far easier. Given all that we don't know that she did not try a navigational tool; simply because LE has not told us doesn't mean it was not attempted.
What I find really troubling is it would seem no one did have HG's back. Someone should have helped her before she reached the DM. It was super easy once she was at McGrady's to tell her to walk on Grady Ave. If it turned into Preston she was going the wrong way. That whole trek to the mall (the running) makes little sense to me. Maybe her friends were just as directionally challenged? One said she "still" got lost and maze of streets was confusing; though to me they are actually in a grid and fairly easy. The numbering is janky but hardly a maze to me at least. All I can say is I hope that ski club was slalom and not cross country.
I agree something pivotal may have happened at McGrady's. I think she may have lost her phone prior to arriving there, and this is why she stays on the wrong course to DM. Remember, it was also reported that someone did offer to help her at the Pub.
The biggest implausability for me in all this is that she would go through all that trouble of being lost; not accept help or ask for directions, then readily slip back into party mode when she meets JM and then drive off with him? He must have had some serious game; quite a different persona than the aggressive oaf with a toe fetish that was painted by Coy Barefoot.