Domitilla is the Latin feminine diminutive of Domitius — meaning "little tame one" or "little one of the household." Saint Flavia Domitilla (1st c.) was a Roman noblewoman martyred for her Christian faith — niece of Emperors Titus and Domitian.
The Catacombs of Domitilla in Rome — Christian burial caves — were named after her.
Domitilla 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 Domitilla reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.