If this movie is made that's what the majority of the movie will be, superficial. Supergirl is not a immediately lucrative character like Batman, WB has shown little interest in Superhero movies other than the big two. So if this is made it will be with as little expenses as possible, they will hire a cheap director and a pretty face. Why? Because studios only see it as a rehash and will treat it as such, they don't look at a Supergirl movie and think "He there's an interesting character with a potentially good story" they think "we could probably make a quick buck". The chances of a talented director with a passion for the source material with a low budget can turn out an authentically good movie is slim to none. I would bet money on it.
Now if they were say going for a Power Girl movie I'd be more optimistic because that shows the studios don't see it as a rehash and may take it into an interesting and original direction.
I'm just sick of people saying "If done right" without considering the chances of it ACTUALLY being done right. If they announced a Supergirl movie tomorrow, right of the back I'd give it a 95% chance of failure.