So tonight Solvi should arrive in Skyhold. I wonder how long it will take her to overcome that "Greatly Disapproves" from Sera for allying with the Templars and start a romance. She's had plenty of smaller approval boosts in the positive direction, so I'm pretty sure that she's still net positive...
I allied with the mages and got a Greatly Disapproves, and that was canceled out very quickly. If you choose the "because it's right" option when taking the role of Inquisitor, that's a Greatly Approves right there. I maxed out her approval well before the game was done. Similarly with Cassandra, I got Greatly Disapproves twice, and was able to max her out as well. I guess it helps that her personal quests are littered with massive approval boosts.
Flirting with Scout Harding also gets you some approval boosts from Sera. Of course, you have to be uninvolved for a while longer so you don't lock out the flirt dialogue.