Extending student visa

Hi, is it possible to extend a student visa for someone who has been in the country for three years? She started on an au pair visa for one year, but has been on a student visa for two years studying below degree level. I understand that you can extend your stay to 3 years with a student visa below degree level, but does this also take into account the time spent as an au pair? Since she's been here on a student visa for 2 years can she continue for another year?

Thanks !