In "Fahrenheit 451" how does the woman act when they come for her books? Why might her neighbor turn her in?

Montag and his team are called into an older lady's house, to burn it and remove the old lady.  She had a house filled with books; her neighbor had turned her in.  Most people have been removed from the houses before the firemen ever get there.  However, the old woman is there, and instead of running out as her house is doused in kerosene, she remains resolute, standing on her porch.  In addition, she refuses to leave.  She even takes out a match herself, threatening to ignite the kerosene if any of them come near her to try to remove her by force.  In the end, it is she that torches her own house. Bradbury writes,

"The woman on the porch reached out with contempt to them all and struck the kitchen match against the railing."

She lights the fire, and burns with her books.  Her neighbor probably knew she had books, and being a good citizen filled with fear, had turned her in.  The citizens of their society were well-trained to fear books, and to fear those that had them.  They knew to report the outcasts and miscreants in their society, as a way of gaining favor for themselves, and protecting themselves from being accused.  I hope that those thoughts helped a bit; for other questions, try submitting another one tomorrow, as the guidelines for this website allow for one question a day.  Good luck.