Wouldn't Becky have to wait for Amber to be doing a livestream to pull that off, though? That's the only way Becky could do it without risking Amber editing it out.Becky should take a page out of Amber's book and be just as cunning. Say something revealing that only she could know, but say it loud, confidently and with a smile. Then, and this is very important Becky if you're reading here---make sure to lovebomb her afterwards, so she's confused out of her mind.
This approach accomplishes a couple things:
1. It reminds Amber--in a subtle way--that her partner has some power here as well.
2. If Becky's consistent enough in covertly shaming her publicly, then Amber learns where healthy boundaries lie, and is now put on notice, that if she dishes it, she better be prepared to take it.