Does she eat the dry food? Do you know anything about her history, if she's been hungry or badly treated at all? Is she a healthy weight? Has she been wormed recently? Does her poo look healthy and a normal amount, probably 1 or 2 a day?
All ours get the equivalent of just under a packet each (we have 5 at the moment and I generally do a 400 g can or 4 sachets between 5) twice a day but one is quite elderly and doesn't eat much and another eats a lot of dry food so only really gets a small amount if she's around when the food is served, which is only some of the time.
They then get free access to dry food and we do go through quite a lot - I don't measure it but I'm sure that if I weighed out a serving it would look tiny, like cereal for humans IYKWIM?
They're all a healthy weight on the above. It's quite rare that cats over eat so you could try giving her a little more as she could genuinely be hungry, or possibly a little anxious about food supply. I've seen that in rescues because they've been hungry in the past.
Aside from having worms, an overactive thyroid is another reason for constant hunger, but I'd hope the vet has discounted that?
What sort of food are you feeding her? Sometimes Whiskas or Felix type isn't very filling, or even makes them more hungry because it's a bit carby, so you could try something with higher protein.
We get a lot of our food from Zooplus but the way we buy food for 5+ wouldn't work for a household with a single cat as it's mostly in multipacks and you have to spend £40 or pay for delivery (we also foster rescue cats and kittens and the amount of food a nursing mother goes through has to be seen to be believed!)
But this is the sort of thing you could try:
www.zooplus.co.uk/shop/cats/canned_cat_food_pouches/smilla/smilla_poultry_pot/110281
www.zooplus.co.uk/shop/cats/canned_cat_food_pouches/rafine/animonda_carny_adult/14033?origin=hopps&q=carny&i=2&ro=1
I don't know if anything like this is available in pet shops where you could just get a couple of cans to try if you don't want to risk buying loads if she won't eat it.