Italian greyhound, I don't think I agree with you, although your argument makes sense.
The reason I disagree is because I believe there should be more conversations about weight and being fat. I think society pushing us into never mentioning it to the person, so they don't get upset, isn't helpful. We know they are fat. They know they are fat. Avoiding rhe subject totally isn't helpful.
And as said, I'm not talking about random strangers, im talking about friends and family members who are unable to discuss it without being perceived as being rude.
The op here doesn't even want to discuss it with her own child. She's went so far as to lie to her rather than admit the truth. She either lacks the intellectual capacity to understand why it's different to telling your kid about Santa Claus. Or is being deliberately obtuse.
How many people have posted here saying they think it's rude for a six year old child to ask her own mother why she has a fat tummy. That's the level of don't mention it we have got to for some people. Like if you don't mention it then it might not be true and no one will notice.
For me it's gone too far now. The whole if you mention someone is fat youre fat shaming. Even when it's a small kid mentioning it to their parent.