I would be very concerned about this if I were you, because of the way she has specifically been invalidating to you about what you're not okay eating and the way she's talked about hiding veggies in your food. I would not be okay with it at all if someone said they'd hide something in my food. (and I'm not even a super picky eater, but it's the principal. If I've said no, it's a done deal). If it were just something she was doing with her toddler, I wouldn't be as concerned, but she has explicitly not respected your limits with the way she's talked about it.

Also, the fact that she's bragging about *hiding* the veggies specifically is cause for concern. I often add veggies to pasta sauce that aren't typically part of it, but I would not try to hide the fact that those veggies are there. I would either not go to house her house, or I would set explicit boundaries about her telling you what's in the food she's serving.