Girlfriend sacked for being pregnant. How long do we have to do something?

Seems 2 years is way past time to think about doing anything. You should have done something when it happened. He did not know she was pregnant so you cannot say he fired her for being pregnant. She was ill and evidently could not do the job. He is not a doctor to know she was pregnant and that was why she was ill. Forget it and move on. Congrats on your son!