Legal Question in Civil Rights Law in Texas

If she is the only one that he told was a prostitute then she likely does not have grounds to sue. Defamation requires spreading that false information to a third party. If other people overheard (not counting employees of the bar) and she can prove other people heard it then maybe she has a claim although the opportunity to recover against the bar is probably less than the cost to pursue litigation. Defamation cases are very difficult to win and if the extent of the harm suffered in stress and depression then that's probably not enough to make it more profitable to pursue those claims than the cost trying to get that case to trial. However, all I know about your girlfriend's situation is what you have posted here. She should talk to a local attorney about her claims.