I think it's quite vague as to if the dark-haired lass looks like Reina or Asuka.
I think Asuka has a longer face.

It's consistent with how Asuka's face was drawn without glasses in s2ep02. Besides, Reina's eyes are normally much more unambiguously purple, while her hair is black bordering on dark blue.

Wahid said:

It's consistent with how Asuka's face was drawn without glasses in s2ep02. Besides, Reina's eyes are normally much more unambiguously purple, while her hair is black bordering on dark blue.

I realized the bangs are what make the clear difference.
Those are definitely Asuka's bangs.
But every other trait is similar.
Considering KyoAni took considerable artistic license with the Hibike Euphonium character designs, perhaps they were going for parallels with senpai & kouhai like in K-On.