"Ki ba'Sadeh Metza'ah". Does this mean that in the field, she is always Patur and in town she is always Chayav?
Sifra: No! The Torah writes "Tza'akah ha'Na'arah ha'Me'orasah" to teach us that the criterion is whether there are people there who could save her, in which case ? irrespective of the location - if she did not cry out for help, she is Chayav,and if she did, she is Patur. 1
How do we know that, if it occurred in the field, the girl cried out?
Targum Yonasan and Rashbam: We don't know for sure; only, since it is a Safek, we give her the benefit of the doubt regarding the death sentence. The husband is nevertheless obligated to give her a Get - due to the possibility that she did not cry out and sinned willingly. 1
Because she has a Chezkas Taharah. 2
Having stated "u'Meis ha'Ish ... Levado" in the previous Pasuk, why does the Torah add 've'la'Na'arah Lo Sa'Asei Davar"?
If the girl is Patur because she cried out but there was no-one to save her, why does the Torah mention a field?
Rashi (in Mishpatim Sh'mos, 22:30): It only mentions a field because it is more common for a rape to take place there. 1
Ramban: Refer to 22:24:1:2*.
Torah Temimah (citing the Rambam): To teach us that, if the act took place in the field, the girl is assumed to have been raped, 2 until it is proven that she was a willing partner, whereas in the town she is assumed to have consented 3 until she proves that she was raped. 4
See Torah Temimah, note 190.
Because there is generally nobody there who heard her cries.
Because had she cried out, people would have herd her cries.
Refer also to 22:24:1:1**.
What are the implications of "ve'Ein Moshi'a lah"?
Rashi (in Pesachim, 25b): It implies that if there is someone to save her, he should do so at all costs 1 - even if it means taking the life of the rapist. 2
Refer to 22:27:0.1:1.