A1) Because, she started to care for him from the beginning while after they had their rocky start (when they first met), she helps him, always sides by his side, help cure his wounds, protect him, and loves him for he is. She even tries to not admit that she loves him, (which she finds that impossible), but she does LOVE him. And of course, during the series, she can be left heartbroken that Inuyasha still has feelings for Kikyo, which causes her to be jealous of Kikyo. But, even despite her jealously towards Kikyo, she accepts that part of Inuyasha will still care for Kikyo. So, after realizing to that reaction of feeling jealous towards Kikyo (EP 48), spending time every day with him and helping him, she realizes that she's in love with Inuyasha.