Sandhya is from the Sanskrit sandhyā (सन्ध्या — twilight, juncture). Sandhya in Hindu tradition refers to the dawn-dusk twilight period — central to the daily Sandhyāvandanam prayer ritual of Hindu Brahmin tradition. Sandhya Shantaram (Vijaya Deshmukh, 1932-2007) was an Indian Marathi and Hindi actress and Bharatanatyam dancer — widely considered one of the figures of 1950s-1960s Indian cinema. Married legendary filmmaker V. Her Bharatanatyam-cinema crossover work is widely studied as one of the examples of classical dance in early Indian cinema.
Sandhya 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 Sandhya reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.