请大佬帮忙解释一下英语句子？

1)She is very nice to talk to .
这句话中为什么不是She is very nice to talk？ 为什么最后还有一个TO？

结构2：名词或代词(主格) + doing
1)My mother cooking in the kitchen, I was doing my homework in my room_ （表伴随）我妈妈正在厨房做饭，我在房间里做作业。