
My 13 yr old colie has always been a pain in the a** re food - though give her a pizza or a cheese butty and she's in 7th heaven - not to mention a Sunday roast LOL.
I've found restricting her time allowed with her food [as suggested already] helps - throw away any leftovers.
She also is affected by the temperature; cold = eat more; warm - eat less - hard to keep on top of but worth it.
Sometimes reducing the amount of food offered can encourage reluctant eaters - so long as they're within the weight range and are fit and healthy.
Another thing I've noticed is that she likes small kibble the best.
I also add small amounts of very smelly soft food to her evening meal; fish, tripe, tripe Chubb, etc but I have to only put in a small amount and mix it REALLY well with her kibble or she'll hunt out the smelly/tasty bits and leave the rest.
A couple of questions - things I've checked from time to time - are her teeth OK? - if there's any problem with teeth it can make chewing difficult - don't know if you do already but try giving her teeth a clean - can't hurt can it?
The other question is whether you have any other dogs/pets? I have strong suspicions that Tinker [my fussy eating collie] also likes to hang on to her food to wind Heidi up -my greedy Elkhound - Heidi gulps her food them drools at Tinker daintily munching on hers!