As you say, the photos could be fake so they don't mean anything. If she was a no-show the first time and she didn't have a good explanation, I wouldn't risk any more money. If you go to Bristol or Exeter, the streets are full of beggars asking for "money for a train fare to get home", it's an old scam, very likely she's playing the same game.
If you've already sent her another £18 for another train ticket, then all you can do is cross your fingers that you haven't been fleeced. Fool me once, shame on you, fool me twice, shame on me.
If she does turn up and things go well, I would shut up about the £18 you lost the first time and put it down to her being a bit flakey. I'd want my money if she was a thief, but I wouldn't care about a mere £18 if it's just a case of her being scatterbrained rather than malicious.