Willa is the feminine form of William — from the Germanic wil (will, desire) and helm (helmet, protection), meaning "resolute protector" or "strong-willed protector."
Willa Cather (1873-1947), one of the great American novelists (My Ántonia, O Pioneers!, Death Comes for the Archbishop), gave the name its modern literary resonance. Today Willa is rising fast in the U.S. and sits in the top 400.
Willa 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.
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In Pythagorean numerology the letters of Willa reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.