Does she change her prices when working from Southend? I think she'll struggle to get the £100 she's demanding for 15 minutes or £150 for 30!!
Personally, I'm always put off when a girl uses the same pictures repeatedly in her gallery like she has. It sets the old alarm bells ringing, as there's no reason AT ALL nowadays in this selfie-mad world why a young woman like her wouldn't have hundreds of unique pictures to post.
You say you've swapped some messages with her. Have you at least spoken on the phone to confirm it's a woman behind the number?