My conclusion is that Alicent (show) does not feel any respect or love for Rhaenyra (and I doubt she felt anything of this before if I'm honest), she is like a rat scaping from a sinking ship... and she would do anything to benefit herself.

And she did this because she would be benefiting with the usurpation right? Well, she was wrong.
So when Alicent (show) realized this, she ran directly with Rhaenyra without any shame, even after the death of Lucerys and after her actions cost her another daughter... to BARGAIN…

Then Alicent (show) play as fool about the righteousness of Rhaenyra when conveniently took the words of Viserys as a miraculous "change of mind" ( NO ONE is so stupid, she was just "letting herself get carried" with that possibility), she knew the consequences of her actions and was ok with it

Not mention that Rhaenyra (show) almost beg Alicent to stop her hostilities against her offering Jace to marry Helaena… Just to witness how Alicent choose to marry her with Aegon II (Hightowers [Alicent included] were always against Targaryen tradition of marrying within family) just for dispice her