Not looking for a flame here, and people may not like it, but just playing devils advocate/defense attorney:
1) Could this be nothing more than an overly chatty FA that wouldn’t shut up, had too much booze, and accidentally spilled a glass on the plaintiffs? And was a messy eater? Anyone who has travelled has sat next to that person that will not shut up, even when you are reading a book. Is this harassment?
2) Is there any chance of exaggeration? sorry for the tough question, but how many cocktails did OP have? Per OPs own post:
On a red eye flight. Need a few glasses of something to send me to sleep! Hope they are serving. Will report back then.
3) Original complaint is about a drunk making wife/infant experience miserable, and is offered/accepts a bottle of Champagne. IMHO, if I was that upset and complained about someone being drunk and putting my wife and baby in danger, the resolution would be to fix the problem. Either move her, or move us.
4) From original post, I see frustration, inconvenience and anger. But where is the tangible danger that this person put your wife and infant in? Was she constantly lifting heavy bags into overhead compartment above them? Was she falling on them? Was she trying to touch/grab either of them?
My guess is that a letter will get some compensation. But it needs to be kept to the facts.
1) A suspected drunk off duty FA was seated next to my wife and child
2) She spilled Champagne and food on them, and in general would not leave them to peacefully travel
3) I complained to the active crew, and they did not resolve the situation to my satisfaction
I apologize if my summary seems to trivialize this issue. But eleven paragraphs, complete with a target number of points in mind, has me in the opposition camp.