If her coat is looking poor, then she is probably missing some vitamins or minerals and I would be more likly to put her on a supplement or a good balencer like Bluechip.
Mollichop showshine might improve the coat, but is more likly to make her fat...
To be perfectly honest I don't think it will make a blind bit of difference to her coat! My friend tried it out on his cob and it just made him fat!!! I think your best off feeding a good balanced course mix which should contain all the vitimins and minerals needed for a healthy shiney coat!
I would agree with nailed. A poor coat would suggest that she isn't getting the nutrition she needs. I would put her on a balancer - I personaly love pink powder, but there are lots of fab ones about. Fast fibre is really good too as it is balanced, economic to feed and no molasses either. Mollichop is stuffed full of added sugar, I wouldn't touch it with a barge pole I'm afraid!! If after she has been on that for a while and along with grooming you are still after extra gleam, then microionized linseed is fab too.