Why do you think your mare should be bred? Since you do not know her true background, she might not be a Fell pony and just a crossbred. Since her previous foal was coloured, I'd bet she might even be some type of Gypsy cross that the owner couldn't feed/sell etc. This borne out by the fact she loves to jump. Gypsies all seem to love to jump.
I'm quite sure she is a lovely pony, but being able to jump and being friendly, is absolutely no reason to breed her. Just this year, I have heard of many, losing their mares and often the mare and baby, during foaling. And all of these were people who were very experienced breeders. I'm tending to feel by your post, that you are not experienced and may be very young.
If you are bent on breeding, what breed of stallion are you considering? What facilities have you for foaling? Have you the money to seek out and pay for, a top quality stud? Have you the money to pay vet fees, should your pony run into trouble, during foaling? What would be your plans for the foal? If a colt, have you suitable facilities to house him separately from his dam, once weaned?
As in many other countries, there is a huge, over abundance of horses in the UK. Many end up on someone's dinner plate in France or - as in the case of your pony, abandoned. It seems to me, she has had a difficult background already. Why risk losing her, since you seem to really love her? Just know, that while she is everything you have noted, her foal might turn out to be nothing like her in looks or temperament. And why add to the population? Responsible breeders are cutting back the number of foals they breed these days. The current economy has not been kind to the horse industry.
Have you pictures of your girl? We love to see pics here.