To properly determine if they are fat, you should check their breast muscle and the prominence if the keel bone. You can't go by weight alone as this can vary greatly from bird to bird.
I know with my slw, she's quite a meaty girl, with some fat, but it's still mostly muscle around there and you can easily feel the keel, but it is not prominent. - if comparing, compare by others of a similar breed or lineage. Hybrid layers can be quite wiry with much less developed breast than their heavy breed counterparts and both would be normal for their body type.
Do check her abdomen as well. Weight gain can also be a sign of acites, as others have mentioned and that is a terminal condition, so you want to rule this out if you can.
Getting a hen's weight under control isn't all diet. They need to be active and able to get around to shift that fat. You may need to lead them in this for a while as there's a threshold where they do become less active due to their weight.