If my daughter was playing, and was good, then at this point in the soccer landscape, I'd look for DA club and not ECNL clubs. I'm probably biased because our older son played DA and know just how much exposure they get compared to everything else.Thank you for that. Yes, I'm looking at exposure based on the big club names. Slammers had a great reputation, but a bit far for us. We are in San Gabriel Valley area.
The link (http://www.ussoccerda.com/2017-girls-club-map) shows which clubs have girls DA. I'd start there. Given that you're in SGV, your option maybe limited to LA Premier or Legends. That said, its not unusual on the boys side to have parents drive their kid well over an hour each way to get him to practices. In particular, I personally know couple of different parents that drove their kids over 60 miles each way, 4 days a week for multiple years to put them onto a top tier teams, including DA team.
So don't just look at the distance but also time involved. If you don't find the fit with DA, then ECNL would be the next step down.
Last, make sure you goto the core club the is actually running the DA/ECNL teams and not one of the satellite affiliate clubs or locations. That means not West, East, South or North or this city or that city version of Slammers, Arsenal, Legends and so on.