hi Hollie, my Alfie is on Arden Grange and has been since he was about 5 months old; he's done really well on it. Arden Grange are very good about sending samples out, if you email or phone them. There are other good makes out there as well - is there any particular reason you were thinking of Arden Grange?
Does your pup have anything else at all to eat apart from the JWB? JWB is a good make, but sometimes some makes suit some dogs better than others.
If you do decide to change her over, it will be best to do it very gradually and slowly over 10-14 days, so I would suggest that you make sure you have enough JWB left in order to do this.