Gna is from the Old Norse Gná (to tower, to rise high). Gna is one of the Asynjur goddesses attested in Snorri Sturluson's Prose Edda (13th c.) — Gylfaginning chapter 35. She is the messenger of Queen Frigg (Odin's wife and queen of the Æsir) — riding her horse Hófvarpnir (Hoof-Thrower) across sky, sea, and air.
Gna 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 Gna reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.