Hi,
I'm assuming she's 14 years old and not 14 months old, right? Since she's an older dog, it could be something with her teeth or health that's just not kicking in her appetite. You are kind of encouraging her fussiness by giving in. But I can completely understand it, esp. if she's dropping weight. You don't want her down to skin and bones. I've heard of senior dogs just wasting away :( Geriatric dogs do have special considerations that youngsters haven't earned ;)
I suggest talking with her regular vet and have him/her give her a complete check up. There is likely some physical reason for this change, esp. if she's always been a regular eater. 14 is a venerable age for any breed. It needs to have the respect it deserves :)
good luck,
toodles