Nidhi (निधि) is the Sanskrit word for "treasure" — both literal and symbolic. The Nine Nidhis are the treasures of Kubera, the Hindu god of wealth.
Nidhi is widely used in India.
Nidhi 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 Nidhi reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.