Steering her heart

I think that Katie meant that whenever Lynn cried, she couldn't ignore the crying. For example, if Katie had an intention to ignore it, and didn't plan on cheering Lynn up, she would do it. But as soon as Lynn would start crying, Katie would forget all her intentions and her heart would change the feeling of ignorance.

There was once or twice when my brother threatened to hit me if I touch his stuff, when I was younger. I had most of the things my brother had, like an iPod, my own shampoo, and my own body soap. My sister though, stole it all and put it somewhere I couldn't find it. She thought I would waste it all. My hair stunk for a week and I didn't want to use my brother's shampoo in case he meant his threat. But after about 10 days, my brother went up to me, hugged me and said he was sorry. He said he had a "change of heart". He told me that when he felt my hair was rough, he gave me permission to use his shampoo, and he didn't hit me after that.

I think that's what "steering your heart" means.