Isidora is from the Greek Ἰσιδώρα (Isidōra — gift of Isis) — compound of Isis (Egyptian goddess) + dōron (gift). Isidora is one of the Greek feminine names — central to traditional Greek + Christian heritage.
Isidora is a compound name. Its parts are dōron — each an attested element with a recorded meaning of its own.
Isidora 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 Isidora reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.