Service recovery hasn't exactly been one of CO's strongpoints. Hopefully UA can help CO out in this regard.
As for what the FA could have done, the FA could have hit the FREE switch for the whole flight. Perhaps a bit of overkill, but it would've made right by the F customers at least. And with the number of people in Y who would have paid for it, processing all those refunds for ~20 F customers would have probably cost the same, not to mention the goodwill generated.
That said, CO employees have had their hands tied for years since Bethune left, so doing something like that and standing behind that decision is not exactly something can be expected with CO's fear culture.
Next best thing would be to document the problem and have CS issue customer care proactive email to everyone in F within 24 hours of the flight a la UA. But as I said before, service recovery is not exactly one of CO's strong points, so assuaging customers is not their forte.
That leaves the next best thing -- pay the six bucks and fight for a refund.