Sounds like you got some good points out there without causing her to head for the hills. Top marks! It probably wouldn't have worked out so easily if the two young blokes had hung around. They probably were relieved to get away and let the two "old ladies" talk. Little did they know... !
I guess that it's almost a rule that there can be no more than two JWs at a door; I imagine that would be overwhelming for the householder. When the car group is uneven in number, I guess you'll get a solo witness doing doors, without the "protection" of a second JW ensuring that no honest conversations break out.