Your friend is out of line. One thing people never seem to learn is that you should NOT judge your friends if you want to keep them! NO matter what they are doing! And keep your suggestions to yourself unless someone asks you for help! I mean, griping about parenting styles is what nice, anonymous, mampedia is for!
My best friend and I have this concept down to a science. When we hang out, our parenting styles are nothing alike. Her kids are free range and bratty. They don't have to do anything she says, they interrupt, they say nasty things at the dinner table, they're always making noise for attention, etc etc etc. She doesn't mind it. She sits calmly by, secure in the knowledge that "that's just how kids act". It doesn't even stress her out. I think she's nuts, but I know she doesn't approve if one of my kids needs to be removed from the scene for a swat for being rude or defiant. Actually, I don't even know it, I just assume it because she doesn't do it, but she has never tried to make me feel BAD for it. And I've never shot her a look for letting her son hammer a hole in the wall, while she was sitting right there telling him to stop banging on the wall.
The REASON we have fun together, is that neither one of us tries to convince the other of anything parenting wise, or gives any dirty looks, etc. We just stick to girl talk in line with how we did for the 15 years we were friends BEFORE we had kids.
No matter what you're judging for, you're wrong to tell your friend what to do or make them feel bad. That is what your friend is doing. She needs to butt out of how your child eats. You're right, she has not walked a mile in your shoes.
People are really weird about food, so I feel for you. I'm one of those, "I don't really care if they eat" parents. If they don't eat their food, they don't get anything until next meal. End of story. I don't care. As long as they sit nicely at the table until everyone is done. But my husband, relatives etc, FREAK OUT if they don't clean their plates and make it a DINNER DRAMA. Drives me nuts. Why do people CARE?
I would explain this to her one more time, prefaced by: "I don't need to defend myself, but, my son has X eating issues, and that's all I can say, so please don't pressure me about this." If you ignore it, and intend to stay friends, she's just going to keep doing it, but if she's just ignorant (but a nice person) and didn't realize she was wrong, this should stop her.