Yaa is the Akan day-name for a girl born on Thursday. Yaa Asantewaa (c. 1840-1921) was the legendary queen mother of the Ashanti who led the War of the Golden Stool against the British in 1900 — among the most famous African resistance leaders.
Yaa is widely used in Ghana.
Yaa does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Yaa reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.