She can love your baby AND respect your wishes at the same time.
Remind her of this. She can get butthurt if she so chooses, but at the end of the day, this is your baby and you make the rules. Honestly, I probably would've laughed out loud at my mother if she made a comment along the lines of "Oh, you're going to listen to the doctorrrr instead of meeee". Um yeah, ma, hate to break it to you but they kind of went to school for it but thanks for playing. I can understand not taking this approach with someone helping you out, though.
Just plan a talk and make sure she knows you love her and are glad for her helping out and getting that extra little bit of time with the baby, but it does not make her a co-parent and there will be serious issues if she goes against what you lay out as the rules.
I totally understand this kind of stuff. Their information was different when they were raising us. My mother (completely without malice!) indulged me with a story of someone who had their child removed from the home because of "failure to thrive" because the mother, like a fool, chose to breastfeed. She genuinely thought this would be helpful to me in deciding how to feed my child because of the attitude towards breastfeeding vs. formula feeding when I was born. You know you're right, just try not to choke slam her when she thinks she's being helpful.