I'm worried about my cat's new weight

My cat's been packing on the pounds these past few months, and I'm honestly kind of freaking out about it. Her vet said she's getting too heavy and I need to watch what she's eating, which... yeah, I probably haven't been great about that.

The thing is, I don't even know if I'm feeding her too much or if something else is going on. She's still her usual self - playing, being goofy - but I can definitely tell she's bigger than she used to be. The vet warned me it could cause real problems later on, and that's been stuck in my head ever since.

So I've been trying to give her less food, but oh my god, the guilt. She cries at her empty bowl, follows me everywhere, and just stares at me like I'm starving her.

I know I need to get this under control for her health, but it sucks making her unhappy. How do I go about this without making it seem like I'm starving her?