Cog,

She will take the Piccadilly Line from LHR, and transfer at either Hammersmith or Earls Court to the District Line. Make sure she knows to take the District Line towards Notting Hill, and exit at the High Street Kensington tube stop. She will exit the station, turn left, walk 10 yards and turn left onto Wright's Lane. The Holiday Inn is about 150 yards directly ahead, and she will literally walk right into the front door. If you land on a weekday she will most likely beat you to the hotel. Have her grab an Oyster Card and put 20£ on it, as it makes all the tube trips cheaper. Departing, just use Google to figure out what time to depart the hotel for her to arrive 90 minutes prior to departure. Your pickup will be 2.5 hours before departure if memory serves, and is about when she needs to leave as well. Pay attention to the 100ml/3.5oz make per liquid bottle and overall max of a 1 liter clear bag for all liquids and gels when returning.

+1 on War Room. Recommend (highly) doing one of the double decker tour busses to start, then figure out where you want to go back to. They are hop on hop off, so no worries on length of time. Some include a boat ride down to the Tower of London as well.