1.She comes here later than me.此处的than当然是介词.
但是也可以表达为:She comes here later than I.此时than视为连词.
2.以上两种表达方法都是对的.
3.楼主的理解很对!后者的确可以稍微复杂一点,变成:
She comes here later than I do.(I是第一人称,当然不能用I does)
或She comes here later than I come here.(有了come here,就不能再加do了)