Good luck at your meeting! As someone who is a director in a US-owned multinational, my advice is as follows...
When you tell them what you're going through, point out that you realize this change will be visible to the other employees and that the company may not have had to actively practice or enforce whatever diversity policies they have in place. Ask how you can help them, as you appreciate the support, help and acceptance they will show you.
By phrasing it this way, you're making a very positive and non-demanding stance while still gently making them aware that you DO know you there is an obligation on them and what your expectations are - all in a way that doesn't sound like an aggressive demand. An HR director should be smart enough to get your message and respond positively to your amenable approach (hopefully you don't have a bigoted arse for an HR director).
The big mistake most people make is blundering in with a confrontational attitude of entitlement which, even if they are entitled, is just going to put everyone else's hackles up and will just be counter-productive.
