1) She used both hands to pick up the phone and move her webcam in both videos.
2) It's a different camera angle. Obviously the reflection of light will be different.
3) It's the same model.
4) Face shape appears to be different because one is looking up, the other is looking down. As for the hair, the first one matches the hairstyle of the confirmed Jiyeon, and the second does not, so is the girl in pink really Jiyeon?
Last, but not least, neither of those are Jiyeon according to CCM, so that twitter link proven her innocence is definitely false. However, in reality, it's Jiyeon in all of those videos.
We have to come to realize that she was young and her hormones were raging. Girls do stupid things at that age. I hope she will be strong.