Tarsilla is the diminutive of Tarsia. Saint Tarsilla (d. c. 581) was the paternal aunt of Pope Gregory the Great who, on her deathbed, reported a vision of Christ welcoming her — recorded by Gregory himself in Dialogues Book IV.
Featured in Gregory the Great's writings.
Tarsilla 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 Tarsilla reduce to 2, The Peacemaker. This is a traditional interpretive system, not a factual claim about the name.