Most people can take a joke but unfortunately it just takes that one a**hole with no sense of humour to ruin it for everyone and there usually always one.
When I worked at Wilkos there was a series of running jokes usually aimed at the girls. Most of them involved items from the kitchen department. We'd say things like "nice rack (insert employee's name)" when they were putting out a plate rack, "nice jugs" when it was pyrex jugs and "you got a nice set" when putting out a crockery set.
My mate John made one of the above jokes to a girl who afterwards gave him a really dirty stare for it. Luckily after he explained the joke she saw the funny side.
I wouldn't make a joke about someone after only working with them for a few days but 2 and 1/2 years later I would think someone would be able to tell if someone can take a joke/comment or not. If the allegations are genuine it begs the question of why were the complaints not made then, not after she has left?
As others have said there are many ways of dealing with issues before resorting to suing. If they have not been explored and there is little evidence to back up the accusations I would not worry.