Waalaykum Salam brother.
To get an answer to your concern I phoned the office of Sayyid Sistani andthey said that: it isn't counted under zina. It's a Gunah I.e. a sin. Since she is asking for forgiveness, it only sounds fair if you gave her a chance. Part of Her repentance would be not to use such social sites where she could fall in the trap again.
Also, I would suggest you both see a counsellor or a Local Aalim for further patch-up, these will put a stop to your worried thoughts and help her revert InshAllah.
You and your family are in my duas.