Bad publicity for United or no, the "girls" don't have much of a legal basis. The airplane was checked over. What more did they want - disassembly?
The complaint was filed with OSHA, which strikes me as something desperate. FAA and DHS had no problem with the airplane being flown, or they'd be involved already. I suspect the f/a's have exhausted all of their company and union appeals, leaving this as the only alternative. Why don't they sue? Most such cases are taken on a contingency basis in the US - and that's likely all these folks can afford anyway. However, no attorney will take such a case unless there's a good chance of winning. That tells us something.
Sorry, but every single party involved said the airplane was good to go, save these flight attendants. Expressing their concerns is fine, but once the aircraft passed inspection they were wrong to walk off.