Yrsa is an Old Norse name possibly meaning "she-bear" — used in the legendary Hrólfs saga, where Yrsa is the queen and mother of King Hrólfr Kraki.
Yrsa is widely used in modern Iceland. Yrsa Sigurðardóttir (born 1963) is a contemporary Icelandic novelist.
Yrsa 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 Yrsa reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.