Hertha is the German form of the Old Germanic Erþō (earth) — an early Germanic earth-mother goddess described by Tacitus. Hertha Ayrton (1854-1923) was the British electrical engineer and suffragist — the first woman elected as a member of the Institution of Electrical Engineers (1899) and the first woman read a paper to the Royal Society.
Hertha 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 Hertha reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.