That depends on where your girlfriend is from and what her past travel experience is. People who have been to the US before are treated more favourably than newcomers.
There's no way to say what % get turned down - you'd have to enquire at the visa section of the US Home Office and they keep this data classified.
Svetlana, 48 y.o.
Sure, it is possible. There are many women, myself included, who successfully applied and were granted B1/B2 visas for the USA. However, in Russia currently, waiting for an interview may take as long as up to a year due to tensed bilateral relationship.
The statistics for denial rate of applications for visitor visas is published regularly on travel.state.gov. In FY2018 it was about 15% for Russia and 40% for Ukraine.