My mom doesn't believe I am severely lactose intolerant and sneaks dairy into my food to "test" me - How do I get her to stop without making her angry?

Hi all,
In my early 20s, I (29f) discovered that I am severely lactose intolerant. It gives me horrible indigestion, nausea, stomach cramps, diarrhea, etc. In addition, it also seems to be tied to my chronic migraines, which I get about 3-4x/month, and increase in frequency if I eat dairy.
When I initially told my mom, she immediately said "Well you were always fine with milk as a child!" My mom is a big dairy advocate for some reason. I pointed out that I had actually really disliked milk, ice cream, yogurt, etc. as a kid. I would literally turn my nose up to a bowl of ice cream as a kid because I would have such an instant reaction. I only connected the dots as an adult when I realized that lactose intolerance was a thing.
Over the past few years, I've been going through an increase in severity of my GI issues and migraines. It's limited me greatly, as I experience extreme nausea/throw up multiple times per week. I've been to the doctor's many times and recently had an endoscopy performed, which discovered intestinal damage. Still in the process of figuring out why that is. But I've really tried to limit my diet to avoid all trigger foods.
For some reason though, my mom refuses to believe me when I talk about my medical/dietary issues. She constantly implies that it's all in my head and that I'm just too sensitive. But I know my body, and I know that I don't feel good! My doctor's have even confirmed there's something amiss. My mom's dismissive reaction really bothers me, but I also wonder if she kinda feels like she "failed as a mom" in not recognizing my dairy intolerance earlier (even though I totally don't see that as a parental failure or blame her at all).
Lately I've started to suspect her of sneaking dairy into my food in order to "test" me. We don't live together, but I go over to her house about once per week for dinner. I often feel sick after eating at her house, and she's made some suspicious comments. Once I was sick and had to run to the bathroom to throw up ~10 minutes after finishing a meal at her house. When I came back from the bathroom, the only thing she said was "I didn't put anything in your food!" I had never thought that before she said it, so it felt suspicious. She never even showed the slightest concern for the fact that I was throwing up/not feeling good.
My dad also decided to trial an elimination diet with gluten years ago, which my mom had a hard time accepting too. She insisted his GI issues, which he had tied to gluten, were all in his head. She even admitted to me that she had been sneaking it into his food to "test" him.
Last night, I was over at her house and actually CAUGHT her putting dairy into my dinner. It wasn't even a necessary ingredient at all, so it felt extra disrespectful and like a verification that she has been "testing" my lactose intolerance.
My mom is a pretty sensitive person, so I didn't feel comfortable calling her out on it in the moment. I knew she would become very angry and it would ruin the night, so I didn't say anything. But I unfortunately had GI issues all night because of it. And this increases my chances of getting a migraine.
The biggest issue is that I feel I can't trust my mom anymore. I honestly feel really hurt and I want to be able to talk to her about it, but she's the type of person that would just get angry and defensive. Does anyone have any insights or advice as to how I can talk to her about it?
TL;DR My mom doesn't believe I am lactose intolerant and I caught her sneaking it into my food to test me. How can I talk to her about it without making her angry?


Source.