Hi Sami,
It would be best to talk to her again instead of randomly adding her on social media.
If you talk to her again, you will hopefully be able to establish some rapport with her.
It will also give you the opportunity to exchange social media information with each other while you are both talking.
This is the more effective way to do it.
If you just randomly add her on social media, it would be too easy for her to deny your request.
Even if she accepted it, being that you didn’t build any kind of rapport with her beforehand, she wouldn’t necessarily engage with you on social media as frequently as you would like, if at all.