Do you think Rain truly loved Spirit? She wasn't nice to him at first and was very hostile and treated him badly, which made me think she hated him, if she did love him what do you think made her change her mind about him?

I think she dint understand him at first and if you think about it spirit dint understand her ether he thought she was acting like a yearling acka a baby but later on there love grew and one day as you saw they were together in sprits homeland

yes of course

She was hostile towards Spirit at first because Spirit was acting like an ass. He charged Little Creek and threatened him and that's why Rain was furious at him.

Of course she does

She didn't like him at first because he was a stranger who wasn't nice to her human.

If yo pay attention to the music montage, you can tell it takes place over the course of several weeks at least. you can tell by the changes in the length of his mane. Short buzzed, slightly longer when little creek tries to paint him/when he meets the little girl, to even longer when he gets rain the apple.

during this time the two bond and spirit learn to love his new life and care for the humans around him. she changes her mind because they get to know eachother.