How to politely decline fastfood from female junior at work ?

Hey everyone. Might seem unusual but I 28F am in a dilemma. Since a few days, one of my freshly joined female juniors is being extra sweet to me at work.

She has recently taken a government residence adjacent to me (the only one available, rest all were already occupied).

She invited everyone to her housewarming lunch yesterday, which she had cooked herself. That was okayish. Everyone else were going and I being the senior to her (and incharge as well), didn’t want to come off as snobbish. So I accepted when she insisted.

Today, she brought samosas for everybody. I’m a clean diet freak. I’ve cut all sugars and fastfood from my diet. And I workout everyday. I smilingly refused and stated her the same.

But then her face fell. And I had to eat alongwith other staff. 🥲

Now I regret it so much. I worked out today too, but it still feels like I’ve gained weight. 😭

How do I politely refuse her and ensure there’s no hostility at work ?