Beau is a masculine english name. Yes it does mean "beautiful" in French. It ranks 311 for boys in the US and 40 in Australia (NSW). Shockingly in England/Wales and the Netherlands it shows up on both charts. For boys 187 and 212 respectively and for girls 275 and 335 respectively.
I see Beau as a boys name and only a boys name.
Also Bo is a masculine swedish and danish name as well as a gender neutral chinese name. Bo means "to live" from its derived Old Norse name (Bui). And Bo also means "wave" in Chinese. This spelling (Bo) actually ranks on both charts as well. In the US, Bo only ranks on the boys chart (at 786). In Belgium its only on the girls chart (at 95). And lastly in the Netherlands it ranks on both charts at 413 for boys and 75 for girls.
I'd rather see Bo over Beau for girls. Altho I still see it as a boys name.
I think of Bo Jackson (NFL & MLB All Star) and Bo Bice (American Idol). I also think of Beau Biden (a lawyer/politician) and Beau Bridges (an actor) when i see this name.
I do see where you are coming from. They do sound like "Bow".