Can I talk to a girl just to ask about her, not for anything else; she is like my sister?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Basically, talking to a girl if she is in complete Hijab or talking to her from behind a screen is permissible provided the talking should be limited to necessary matters and it should not be in seclusion. Allah Says (what means): {… then do not be soft in speech [to men], lest he in whose heart is disease should covet, but speak with appropriate speech.} [Quran 33:32]

In the above verse Allah forbids being soft in speech, not the talk itself if it happens within the limits set by the Sharee’ah.

However, if a Muslim feels any inclination to a non-Mahram woman, even in the presence of her Mahram, then we advise him to put an end to this inclination at that early stage. This is because it can be the first step to temptation by Satan if he does not cut it off; no doubt, it may lead to more serious acts. Allah Says (what means): {O you who have believed, do not follow the footsteps of Satan. And whoever follows the footsteps of Satan - indeed, he enjoins immorality and wrongdoing.} [Quran 24:21]

Allah knows best.