The ex needs to adjust to the new reality of coparenting.
At its utopian best, ordinary day-to-day coparenting allows respectful, reciprocal team work between separated parents. At worst or very most basic, seperate parenting with no involment or influence from the other. (Different story of course for actual neglect and abuse).
In a nut shell, she can harp on about your parenting performance to all and sundry, in whatever tone and on whatever trivial matter she likes - all of no consequence to you. Marriage is over. You're no longer operating as a team in that old sense. Neither of you can dictate the terms of day to day parenting to the other. Simple as that. You can choose to allow her that control, or you either ignore completely, or send through banal, empty responses. Once things settle down, sure there's scope to Reciprocate requests ect, but until then, shut it down - you are not operating as a team.
Once upon a time, my ex and I couldn't comment, judge or even request a single thing to each other regarding parenting - trivial or semi-serious. He wasn't taking it from me, nor I from him. Even my solicitor laid it out bluntly: "I won't be engaged to argue on your behalf about why your ex has again forgotten to pack your child's teeball shoes".
To be honest, it took a long time for me to gain perspective. But now, ex and I are able to amicably exchange texts about anything such as how much screen time is best, despite having different views on it, and weirdly find ourselves in peaceful middle ground.
An FVRO can address the relentless harassment, sure - but I agree with previous posters that it's a poor long term strategy. If it were me, I'd simply document and file any real impact her questioning is having on the child, and flat out ignore the rants/demands about your parenting. It's white noise, and irrelevant to any future court case (again - unless there is actual neglect or abuse).
My Mum used to give us the Spanish Inquisition each and every time we returned from Dads house growing up. Every time, without fail, from the age of 7. Dad never did it. My siblings and I have never forgotten it. Kids know. They learn, and they soon start resenting the behaviour.