Legal Question in Civil Rights Law in California

Your friend, not you, could argue and claim gender and reverse discrimination, as long as she understands that a plaintiff has to prove the job action was based on discrimination that is illegal under the various civil rights laws, instead of simply due to 'office politics' and favoritism, neither of which is illegal. The company denying your friend an application was allowable, especially when based upon 'non fraternization' policy. Such policy was violated by allowing someone else's friend to apply, but that doesn't make it 'illegal', only political or nepotism. In addition, your friend would be running afoul of the pro-homosexual discrimination rules. That homosexual friend would have a much better case than your friend, had they been the one rejected instead of your friend. I'd take that case, but probably not your friend's, at least not without credible, admissible, evidence in witness testimony or documents to show the rejection of your friend was "because she was female".

If you

I think this is an extremely tough case to prove.

To prove actionable discrimination, your girlfriend would have to show that she belonged to a protected class. It sounds like you are trying to make a case out for discrimination based on sexual orientation, which is indeed a protected class. Claims of discrimination against heterosexuals, however, are extremely difficult to prove. Moreover, companies are allowed to make exceptions to policies, without it constituting discrimination against others to whom the policy is applied. As such, it would not be sufficient to allege that there was an exception made to a policy. In addition, it seems likely that the company has hired other heterosexual personnel, including you. This fact weakens your girlfriend's case.