Hello, darling!
Being overwheight is not a health issue. Not at all. Being overwheight is not being sick. Your mom is completely wrong and fatphobic. You’re not being oversensitive, she was actually acting like being overweight is an insult or something bad, which is not.
Whether you’re overweight or not, what you’re mom is doing is wrong. She is not telling anything that is worth caring for. You’re so beautiful the way you are and she has not the right to say something like this to you or to anybody, my dear, no one should be called overwheight as in insult. The world is not the way she thinks it is, and she will have to learn or stay in ignorance forever, and this is not on you, okay? Never.