I really feel for you! Tough situation. I bet you'll get some helpful tips. I remember my ex and I thought we knew it better until we had children of our own. I was so jealous!
Anyway, some thoughts...don't know how useful, but write all tips you get that speak to you in a notebook and refer to them, for strength, as needed.
Paraphrase what you hear her tell you, back to her in the way you understand it.
Breathe deeply. You are listening, you have heard her.
You can comment, "That's something I'll have to give some thought." "That's interesting." "I hadn't thought of that." "Baby, did you hear that? You have a smart, great aunt! Mama will consider it if she ever gets a minute!"
When baby is asleep. you and your husband can ask her her opinion on parental issues. Opinionated people love to give their opinions.
Try I feel statements. I feel good about how I'm feeding him. I feel that's something to talk about when you and I are having a chat. Later, I feel it's okay for him to eat his dessert first, if that's what he wants, because there's no real reason he shouldn't. I feel you're second guessing me when you say those comments in front of my son. I feel it's best you tell me when we're alone because I want to give him my attention and he may feel the tension I'm feeling.
As to how you think she might feel about your husband....Maybe she can help by giving you some alone time with your husband. "I feel your aunt thinks..."
Hang in there! Breathe deeply and enjoy your husband and child. Hopefully, Aunt will act nicer if she feels you are listening to her.
Best,
G.