Cressida is from the Greek Khryseis (gold, golden) — the daughter of Calchas in the Trojan War cycle. A vintage Shakespearean name in the modern revival. Troilus and Cressida (1602) — Shakespeare's problem play; Cressida is a Trojan woman whose love for the Greek prince Troilus and subsequent unfaithfulness with Diomedes became one of the most-debated examples of female inconstancy in English literature.
Cressida 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 Cressida reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.