OP I don't think anyone here thinks it is okay for you/anyone to suffer racial/ any other sort of abuse from a stranger.
But it's also not okay to send anonymous emails to someones place of work ten months later when you have no proof and no witnesses and it didn't take place at the workplace or while she was in uniform.
And can you be sure, after all this time has passed, that she is the same woman? After all, you say you felt shocked and victimised and alone and I imagine that it was very stressful for you. Stress sometimes affects the way you remember things, especially when time has passed and it may be that this woman just looks similar to the one on the bus.
And I say this because I suffered a mild panic attack in the supermarket on Thursday because I thought I had seen my FIL further along the aisle. It wasn't him, poor man didn't even look that much like him when I had a proper look, but he was about the same height and build and had the same colour hair. And after that, even though I knew it wasn't FIL, when I caught a glimpse of the man again I still felt panicked and ill and (very unreasonably) like this man was somehow linked to FIL and so someone to be afraid of.
For that reason (possible mistaken identity) it is not worth the risk of reporting her. But on a more serious note for you, it may well be that they do take your email seriously but against you rather than her, report it to the police to be traced in some way and get you warned or prosecuted for harrassment.