Moomanchu,
There is no published statement of "no field service/no salvation. But there is a "scriptural principle" used by the Washtowel Blabber and Trash Society:
(Ezekiel 3:17-21) 17 "Son of man, a watchman is what I have made you to the house of Israel, and you must hear from my mouth speech and you must warn them from me. 18 When I say to someone wicked, ‘You will positively die,’ and you do not actually warn him and speak in order to warn the wicked one from his wicked way to preserve him alive, he being wicked, in his error he will die, but his blood I shall ask back from your own hand. 19 But as for you, in case you have warned someone wicked and he does not actually turn back from his wickedness and from his wicked way, he himself for his error will die; but as for you, you will have delivered your own soul. 20 And when someone righteous turns back from his righteousness and actually does injustice and I must put a stumbling block before him, he himself will die because you did not warn him. For his sin he will die, and his righteous acts that he did will not be remembered, but his blood I shall ask back from your own hand. 21 And as for you, in case you have warned someone righteous that the righteous one should not sin, and he himself does not actually sin, he will without fail keep on living because he had been warned, and you yourself will have delivered your own soul."
w948/15p.15ThisGoodNewsMustBePreachedFirst19
Of course, preaching from house to house to strangers is no easy matter, regardless of how many years one may have been a Witness. Then what keeps these Christians going? Their Christian dedication and a sense of responsibility. Paul wrote: "If, now, I am declaring the good news, it is no reason for me to boast, for necessity is laid upon me. Really, woe is me if I did not declare the good news!" True Christians have a message that means life, so how could they possibly keep it to themselves? The very principle of bloodguilt for failing to give a warning in time of danger is an impelling reason to preach the good news.—1 Corinthians 9:16; Ezekiel 3:17-21.
w869/1p.27GodlyRespectforBlood
(Ezekiel 3:17-21; 33:7-9) Jehovah’s anointed servants and the "great crowd" of their companions bear a similar responsibility today. Our witness should be thorough. Thus, during the day of God’s vengeance, we may be saved along with those who listen to us.—Isaiah 26:20, 21; 1 Timothy 4:16; Revelation 7:9, 14, 15.
km2/97p.1ShareIntheWorkThatWillNeverBeRepeated 4
We must share in sounding the modern-day warning to others, "whether they will hear or will refrain."
This is a God-given assignment, which we dare not ignore. (Ezek. 2:4, 5; 3:17, 18)
As you can see there is no definite statement that "Door to door" is required, simply that we warn others. Let your mother off the hook, in reality she's in good shape by this legalistic standard. You don't want to pressure the old gal to waste her time and gas do you?
W.Once