"Yes it is a boys name, but if people can get away with naming their girls Ashley, Jordan, Hayden, Cameron etc then why not Darius."
I don't think "everybody else is doing it" is powerful reasoning.
Your daughter may have to live with this the rest of her life. Deed polls are an expensive faff and ime, by the time I was old enough to get a deed poll change, I'd got so used to being called by my name, that no other name sounded right either.
In addition, plenty of MNers with doctorates apparently regularly experience disbelief on the phone that they are who they say they are. (Because apparently only men can be doctors
).
How much worse is it going to be for a girl called Darius?