A similar thing happened with Tilly when she was younger. A number of people told me she was getting a bit porky (including the vet and people at ringcraft) and I got quite worried. However, a lady I know locally who breeds cockers told me that, if anything, Tilly could take a bit more weight as she liked her puppies nice and chunky too. I totally respect her advice, so did not cut down Tilly's food and carried on with normal exercise. Now, at 14 months she is, if anything, a bit too lean (she weighs 9.8 kilos, but is on the petite side). She is very fit and healthy and has as much to eat as she wants. So, as others have recommended here, I wouldn't worry about it - carry on as normal and I'm sure things will sort themselves out when Jenni is older.
Sue and Ms Petite