The only times Chris was even remotely interested in Stacia was when he was under what’s her name’s spell and maybe a little when his memory was gone but even then he realized he belonged with Tayna. He even tells Tayna that and explains he likes and trusts Stacia because she’s been nothing but honest with him, up to and including how she feels about him and how she thinks his relationship with Tayna will fail. She then drops into the background to wait.
And if you are paying attention, there are several small incidents when Stacia is more than a little aware of Declan and you can see their friendship building, starting with the training in the empty building. You can also see how she’s starting to care for him when she finds out what his life was like and is like. As far as their romance, John spells it out when he says her wolf has called it for Declan. It just takes Stacia a little bit of time to realize/admit what’s happened.