there is no kik Messenger for pcs as you can read on their official website. but there is a demand for it, so there are a lot of malware websites just waiting for people like you, so be careful.
the only way to get this running is using the original Android app with the Bluestacks Android emulator.
the best messenger for her is the one her friends are already using.
not sure what you mean with "the one Win8 has built in". Windows Messenger has been abandoned since a while. Skype on the other hand is not a bad solution as it is available on all major platforms. http://windows.microsoft.com/en-us/messenger/messenger-to-skype