Blanche is from the Old Germanic blank ("white, fair") — adopted into Old French as blanche. Blanche DuBois — Tennessee Williams's tragic heroine in A Streetcar Named Desire (1947); her closing line "I have always depended on the kindness of strangers" is one of the most-quoted in American theater; Vivien Leigh won the Academy Award for Best Actress for the 1951 film (directed by Elia Kazan); the role has since been played on Broadway and major stages by Jessica Tandy (original 1947), Tallulah Bankhead, Ann-Margret, Jessica Lange, Patricia Clarkson, Gillian Anderson, and Cate Blanchett. Blanche Bates (1873-1941) — American Broadway actress.
Blanche 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 Blanche reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.