Susan is from the Hebrew Shoshannah (lily). Susan B. Anthony (1820-1906) — American suffragist who alongside Elizabeth Cady Stanton founded the National Woman Suffrage Association, was arrested in 1872 for voting illegally, and whose face appears on the US dollar coin. Cancer Diary author and AIDS activist.
Susan 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 Susan reduce to 2, The Peacemaker. This is a traditional interpretive system, not a factual claim about the name.