Hi
K2 running club is not a UK athletics club, it is run on Tues and Thursday evenings (6-7pm) and Saturday mornings after the Parkrun in Tilgate Park and most runs are on the track at K2. The focus is pretty much on interval and speed sessions as it is generally all track based, therefore you may not want to go to all sessions in a week! It is an inclusive group and caters for all abilities, you just turn up and run - you don't have to be a paid up member you just pay for the session at the reception like any other activity at K2.
Saints and sinners - I am not sure if they are still about as I have also been looking for a club in the area and have been unable to find any contact details also. I went along to Horsham Joggers and they weren't the most friendliest bunch (not a Horsham dweller
). I have also been along to Lingfield RC who are a really friendly bunch - however it kind of depends if your fiance wants to drive over there.
Let us know how she gets on.