Susannah (שׁוֹשַׁנָּה) comes from the Hebrew shoshannah, meaning "lily." In the Old Testament Apocrypha, Susanna is the heroine wrongly accused by two elders and vindicated by the young Daniel.
Susannah peaked at #225 in the U.S. in 1985. Stephen Foster's 1848 song "Oh! Susanna" made the name an American standard.
Susannah 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 Susannah reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.