How would you approach this situation?

Amanda

So my MIL has been giving my 10 month old straight apple juice and it has caused some funky bowel movements. I don’t think I’d mind if she’d asked me first so I could remind her that it needs to be diluted but nope, just straight up juice in his bottle. How would you ask her to stop? Our relationship is great, never had any issues but I HATE confrontation on any level and was wondering how I should approach this.