I wouldn't as the nutritional balance will be wrong for a full-grown cat. Once in a while it is fine but adult food is better to be fed all the time. Some cats are just small - My Willow was 2.5kg. As long as the vet is happy with her health, I would just carry on as long as she is eating well.
If she doesn't eat any dry food at the moment, some might help as it is high in calories. I would definitely stick to higher quality food, especially if she doesn't eat a lot. Hill's science plan is quite fattening.