I don't know what brands are available where you are, so I can't really say.
Is it a dry-food or a wet-food that you feed her?
If it's wet-food, consider mixing in some dry-food too.
Also consider whether it's a Gravy or Jelly, since that can make a difference too.
And you might want to maybe experiment with flavours. One of my older cats for example was always quite sick with Fish based Foods, like Tuna.
If you feed just a dry food, changing to a wet food may also help.
And it doesn't have to be branded, either.
If your local Supermarket chain happens to sell it's own home-brand Cat Food, those may be worth trying too.
Cats can be quite awkward when they get sick on their current food, since it can mean making a lot of tests and changes.
And they won't always stick to one diet. So bear in mind that it can happen multiple times over the years. My cats have gone in and out of favour with certain flavours, food types and brands many times.
You may also consider her feed schedule. Does she get fed multiple times a day? If so, try only once a day.
And try not to feed her any scraps from the table or whatnot.
If the cat seems happy and spry for the most of the time, don't worry too much about it. It would appear to just be a dietary problem.
If she's still got an appetite and is active, then I wouldn't worry about any other medical conditions.
If cost is a problem, which it easily can be (Cat foods, particularly specialiseds can be damned expensive), then don't try buying loads of tests at once.
Just change the diet to another brand/type for a short time and see how she goes.
If she's happy, then continue on with it.
If she continues to be sick on it (give it a couple nights) then test another one.
If you buy them in small packs, or individuals to begin with, and then when she's happy you can buy in larger quantities, to save you wasting money on something she doesn't like.