Sassui is the heroine of the Sindhi tragic-love epic Sassui Punnhun — one of the four most famous tragic romances of Sindhi-Punjabi tradition. Sung in Sufi qawwalis to this day.
Sassui 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 Sassui reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.