Since u have about a week, try visit the following places:
1. Nairobi National Park approx 20min from the JKIA airport (that is on a good day without the perennial traffic) also visit Amboseli or Tsavo as opposed to Masai mara you wont regret it.
2. Fort Jesus, Mombasa while there you can visit the sandy beaches and take a tour of the city and again if time allows visit Lamu, a wonderful picturesque town that has only one car. Malindi and its rare bird species would also be a worthwhile visit.
Kenya is lovely and your bound to enjoy it.