She's totally playing you man.
It's like giving a customer a free drink at a bar or free tokens or even a complimentary room at a casino.
It's all about keeping you on the hook so you'll spend more money.
Maybe it's not a "scam" per say but you're definitely not going to get free sex out of this deal.
You would see it if you weren't in the midst of it, had you read this on someone else's post you'd be thinking "how can he fall for that?".
Now, that much being said, sure there's always a chance that me and the other naysayers on here are wrong and this sex worker sees something in you that she hasn't seen in a zillion other guys just from chatting on the phone and exchanging some genitalia pictures. But it's rather unlikely.
You're going to go meet her if you've got the chance, no matter what anyone here tells you, and I don't blame you. Don't go into the meetup with anything in your pocket you can't afford to lose, and expect to come out of it with an STD if you aren't careful.