Why should she expect this treatment? I've seen folks board planes with assistance who were almost dead, then fly by themselves to their destination without issue. Their wheel chairs were folded up and stored until they landed. If she's a Thal. baby, then she's been around awhile and has probably flown before. (I know that this is an assumption, but no more than your assumption that she wouldn't know the deal. And no more than another poster's assumption that she's sued before or that she's even a Brit. Heck, posters here are assuming that she just now filed the suit, when it may have just now been settledafter being filed years before.)
There are silly lawsuits, and then there are those cases that lawsuits were intended to deal with. I don't understand why so many assume the worst. (OK. Yes, I can see why. But it's still not a reasonable habit.) Yes, there are @sses who look for every excuse to sue, but there are also real people with legit claims.
I do not think her expectations were legitimate and do not think her suing the airline because of their refusal to board her is legitimate either.
Now if her lawsuit is that the Airline caused her distress by their rudeness in addressing the problem; that is another issue; although, we do not know what 'she' said. . .before 'they said'.
We could also maybe allow that the 'insensitivity' of this airline rep; may have been the result of her being taken by 'psychological surprise' here. . . .
Paris to New York; while not a 'sky marathon'; could certainly pose some herculean-like challenges, nonetheless. . .and at the psychological expense of the other travelers and/or/if only. . .the 'crew'as well. . .should we get real insensitive, here.
This woman needed an assistant; and still maintain; that her expectations to travel solo, were surely meant to challenge (financially) the airline; for whatever reason. . .