Duke of edinburgh would be my suggestion, along with paddlesports.
I started kayaking when I was 13/14 for my DofE Bronze, I'm 22 now and a coach :) However I think you may mean she has been canoeing and is scared of capsizing a kayak? That's generally what people are scared of! The Nene's club is quite good apparently, my canoe club visit the nene regularily and a lot of our paddlers have done their whitewater courses there (we're in East Essex, it's our nearest whitewater centre!) And going through a club is safer as they will have coaches who can teach her from scratch the right way to do things, including capsizing. Not only that but on the paddlesports syllabus these days you have to Canoe and Kayak, so they'll teach her both disciplines until she's advanced enough to choose just one [if she wants to choose that is]. Paddling can be pricey though so don't go all out and get a boat/paddle/Bouyancy Aid/etc until she's been doing it for a while and won't give up, the club provides those!
Another sport is climbing, brilliant for core muscles like paddling is and great fun, it would also encourage her to save money to buy some equipment like paddling would. Northampton area has a good few climbing clubs too which look good and active.
Knitting would be good too, it's very relaxing and some suggest that it's similar to meditation in that respect!
I think DofE would be your best bet though, then she'll start a new sport, do some voluntary work, meet new people learn some new skills, do some camping and walking and so on, it's great fun and I am going to try for my Gold once I'm settled again :) Try to find her a club that isn't associated with her school, as it means she'll meet people she hasn't had a chance to meet yet and be independant from her classmates a little.