the more I think about this, the less makes sense. Bear with me while I sperg.
Amber sets up her phone on the tripod in the den and starts her vlog. She's smiling and seems happy. At some point she stops recording for whatever reason and leaves the phone on the tripod in the den.
The same woman who claimed, in her birthday vlog, that she got a text from Becky while she was peeing. This person, who can't even go to the bathroom without her phone, left said phone on a tripod, in a different room.
Becky happens to come across Amber's abandoned phone, turns it on and does her heart to heart in hopes that Amber will upload the video without noticing the part she added?
Kind of hard to believe since Becky has been chained to Amber 24/7 for at least two months now. She has to know Amber "edits" her videos.
The other option is that Amber knew Becky was going to do what she did, but even so decided it was a good idea to post clips before and after of herself being chirpy and smiling.