Nik,
If you know her Gregorian birthday as it seems she does, then you use that birthday date. When all said and done, this is the actual date of her birth!!! I really don't understand the fascination of all this lunar stuff, it's a load of twaddle and does nothing but confuse the issue, ....so just forget the twaddle and stick with the international recognised system that Everyone knows and understands!!!!
Or, .....stick to the birthday that you stated, but only ONCE!! On the Gregorian calendar.....
David......