Hello and welcome to the forum. I am sorry to hear about your Lakeland's colitis problem. A few years ago one of my terriers had it for quite a long time (until she died) so I know how awful it is. I recall that my dog eventually needed ongoing medication, including courses of Prednisolone (steroid).
I wonder if you could supply us with some more information?:
I see you have consulted your vet and your dog has had medication. Did he or she say what was causing the problem?
Have you noticed any trigger factors?
Between bouts of colitis, what is her general health like?
Colitis can be exacerbated by food substances but the devil is in the detail - finding out what it is that is causing the problem. To this end, many vets would prescribe an exclusion diet where you start with food that has ingredients that are known not to cause intolerance. Gradually different things are added in and the dog's response noted. This can take several months and it may be helpful to have the support of the veterinary surgeon or veterinary nurse.
Regarding the Burns Sensitive, is it the one with pork and potato? If so, having just checked it does have cereal in the form of maize: Potato (35%), Maize (27%), Pork Meal (17%), Pea Starch, Peas, Pork Fat, Seaweed, Vitamins & Minerals.
If your dog is having problems with grain this might not be the best food for her due to the maize in it.
I have read that wet food is better for dogs with this sort of problem (sorry, I don't have a reference for that). There are quite a few grain free wet foods and these can be located by use of the filters on the Dog Food Directory of this website.
My friend who has a Chihuahua with colitis has had very good results with Natures Menu Country Hunter wet food in tins. Since starting this in the autumn of last year he has had only one bout and that was brought upon by the medication given by the vet for kennel cough. Another grain free wet food can be found in the Wainwright's range at Pets at Home.
If you check out the Naturediet website here
you will see the frequently asked questions and one of them refers to colitis. To the right of the page there is a link for information documents which are very helpful. Naturediet does contain a small amount of rice and while some dogs can be sensitive to this, many are not. Naturediet Sensitive has the advantage of containing very little in terms of additives - their recipes are quite plain, which can be an advantage when trying to find out what the dog cannot tolerate.
One other alternative is to consider feeding raw food. This is quite easy these days due to the complete meals that some companies are manufacturing e.g. Natures Menu, Natural Instinct and Nutriment.
As David says, grain/cereal is often thought to be suspect in cases like yours but there are others, including certain protein sources such as chicken and poultry.