I have been to UK twice with tourist or visitor visa. In the application form ,theres a question that ask, when do you intended to go to UK, and also during the interview , the EOC asked me what is my purpose of coming to UK. Your visitor should demonstrate to the ECO that she have no intension to overstayed in the UK and that she will abide in the rules that as a visitor she is not allowed to work and that she is going to leave UK on or before her visit visa expires.
I hope this helps. Goodluck.