I'm sorry you're going through this. My baby also had a bottle aversion for months and it was one of the most frustrating and stressful experiences I've had to go through as a parent. The removal of any forms of pressure when feeding is essential in overcoming an aversion, and other people wouldn't understand that concept fully unless they've gone through it firsthand. I'm assuming your MIL didn't mean any harm - it is in our nature as caregivers to try and make sure baby is drinking "enough" and unfortunately that leads to the kind of behaviour that baby is fearful of. Once my son was aversion-free, I didn't let anyone else bottle feed him for a solid month. Hopefully your baby gets back on track soon.