Marcella is the Italian feminine of Marcello — from the Latin Marcus, possibly from Mars (god of war). Saint Marcella (c. 325-410) was the Roman noblewoman who turned her palace into a Christian monastic community.
Marcella Hazan (1924-2013) was the Italian American cookbook author who introduced authentic Italian cooking to America.
Marcella 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 Marcella reduce to 2, The Peacemaker. This is a traditional interpretive system, not a factual claim about the name.