Rhonwen is from the Welsh Rhonwen — rhon (spear) + gwen (white, fair, blessed). Rhonwen (anglicized as Rowena) is the Saxon princess in Geoffrey of Monmouth's Historia Regum Britanniae (c. CE). Central to the Arthurian historical-mythological cycle. Subject of Sir Walter Scott's Ivanhoe (1819) where Lady Rowena is the Saxon noble heroine. Welsh + Anglo-Saxon feminine name.
Rhonwen 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.
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In Pythagorean numerology the letters of Rhonwen reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.