Drusilla comes from the Roman family name Drusus — possibly meaning "strong" or "firm." In the New Testament, Drusilla was the Herodian Jewish princess who married the Roman governor Felix and heard Paul preach (Acts 24:24).
Drusilla is widely associated with literary characters; Drusilla in Buffy the Vampire Slayer is the contemporary fictional bearer.
Drusilla 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 Drusilla reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.