Oregon, a state that borders Idaho, has every name given to a child born in that state between 1961 and 2003 on the web:
http://www.dhs.state.or.us/publichealth/chs/babyname/babyname.cfm
If you check the above you will see that there was only one girl named
Nerea born in Oregon in that entire period, in 1987.
For the years 1999 and 2000 only,
Michael Shackleford was able to send me lists based on the Social Security administration data that included all names given five or more times in the USA as a whole. I only can readily find 1999 at the moment, and so can tell you that there were fewer the five girls named
Nerea born in the entire USA in 1999. I will try to remember to look for the 2000 list at home this weekend to see if
Nerea occurs on that one.
In checking my lists for the state of Nebraska, I found one
Nerea born in the year 2000, but none born in 2001, 2002, or 2003. (I still haven't been able to get them to send me the 2004 data yet!).
So though I really can't answer your question completely it does seem that
Nerea is quite rare in the USA. Have you tried writing to the states of Idaho and
Nevada (which I think also has many residents of Basque origin) directly?