I'm going to let the fine folks in HIV answer about HIV (though there's no risk) and will address the STD questions that I'm sure will come later -
There is no risk for any STD from this. Fingering is not a risk for any STD or HIV.
Did someone actually say she had a high viral load, or is this a fear of yours? It doesn't matter - her viral load could be sky high and it would change the risk from fingering - but this doesn't sound like something someone would say.