Assuming you are traveling in a company of 3, 2 adults and one 4 year old, I would never pay the extra buck for PE. PE costs 2x compared to Y and isn’t worth it.
AF has the most horrific seats in PE, both on the B777 and B787. I haven’t tried the A350 in PE, neither I have tried on Delta.
It is so bad that I always hope I won’t get “upgraded” to PE on AF because I prefer Y by far.
Yes SkyPriority is a part of PE but traveling with a small child also grands you early boarding.
The food should be “upgraded” but looking at the reports that upgrade is minimal and not worth the money.
Plus, when traveling with a small child in a row of 3, gives more room for the remaining 2 adults. If catering is important then I would invest in upgrading the food in Y by ordering a special festive meal that cost 28 EUR (or approx) so you have a nicer experience there and keep the big buck in my pocket and spend them on holiday in a nicer hotel or something else.
A plane isn’t silent and also in PE or nearby can be crying babies. That’s just how it is.
You can consider buying earplugs for her or soundproof earphones if it’s critical. But probably a child will sleep anyway with the parents so close.
The child will love flying long haul anyway and she will have an incredible experience.

Have a nice holiday