As virtualwaster says, there is plenty of info on STIs on this board, have a look around. Nobody on here could verify that she is STI free. She may have been fine when she saw a UK punting member, let's say a month ago, but then contracted an STI from the very next client she had. If that's the case and she hasn't any symptoms or been tested since this hypothetical event, then her clients are at risk. Therefore, the very best anyone on here could tell you is that they have seen her and not contracted a dose.
Her enjoys list does not include any high risk activites in terms of catching STIs. She has been an A/W member for going on 4 years and has stacks of positive feedback, so my guess would be that she is experienced enough and smart enough to get tested regularly. But none of that means anything if you're out of luck on the day you visit her.