I would avoid London until after the Olympics....Many European countries are typically historical, alot depends on whether she wants to visit castles and manors, or does she want to do a pilgramage of all the cathedrals and churches.
London: Westminster AbbeY,St Pauls Cathedral, The London Dungeon, Catch a London Broadway show, Soho London, Picadilly Circus, pub hopping, Haunting Tours
Paris/France/, The Louvre, Versailles, The Bastille, Arc de Triomph. The Loire Valley,Notre Dam
Rome Colosseum, The Catacombs
City bus tours are always available in all these places.
Remember that England does not take Euros, though Ireland does....
The best bet is to pay for purchases through a debit/credit card. If she uses an Atm , especially in England cash on small amounts, so she wont have to worry about, trying to get a proper exchange. Banks in England will not exchange Euros for her either....