Workinprogress, this grown man has seen some young and impressionable QFers in their early twenties talk very differenty 10 and 15 years later. I am also in proccess of writing a book on QF, so I do have an interest in the subject beyond your implied charge of my being an idle busybody.
About asking for Biblical instances where women used birth control and using the Bible's supposed silence on the issue as "proof" that it is sin to use it, that is called arguing from silence.
Argument from silence has famously been used by skeptics against the virgin birth of Christ. Paul, for example, does not mention the virgin birth, and skeptics therefore argue from his silence that he did not know of it. If this argument is used as an attempted proof of Paul's ignorance, it is incorrect, because ignorance is only one possible reason for Paul's silence; it's also possible that he did not think the virgin birth was important or relevant to his reasoning, or that he referred to it in texts that have now been lost or mutilated. However, the argument from silence is not incorrect if it is used to prove that Paul may have been ignorant.
Similarly, arguing from silence on the issue of contraception in the Bible proves nothing. Yet arguing from silence is typical of movements that have very sloppy theology at their base; they try to use silence as proof when it is not at all.
Arguing from silence can also become a very slippery slope. For example, the Bible gives no instance of a woman using a computer, but that does not stop many QF adherents from using them. This also shows radical inconsistency in applying the idea that if the Bible does not directly speak affirmitively of a thing, then that thing must be sin to use.
But the Bible may not be silent on showing a woman using birth control. From Song of Solomon 7:12:
Let us rise early and go to the vineyards;
Let us see whether the vine has budded
And its blossoms have opened,
And whether the pomegranates have bloomed.
There I will give you my love.
That the couple is going to have relations where the pomegranates have bloomed is very interesting.
Pomegranates were used as birth control in the ancient world. The entire fruit and its blossoms contain a phytosterol almost identical to progesterone, the homone used in birth control pills. When pomegranates are taken they act similarly.
In Egypt, archeologist have even found pills of ground pomegranate seeds.
As well, the scooped out hard shell of a pomengrante husk is mentioned in some ancient literature as having been used as a diaphragm.
Also, the ground pulp of pomegranate, when both smeared on to a man and inserted into a woman, rapidly produces lactic acid which is as an exceptionally efficient spermicide.
Let me say that there is nothing at all wrong with wanting and bearing many children, if God has so called a couple that way. However, using QF theology as a basis for that can be very problematic because the theology is itself very problematic.
But our job is to repsond to Him in an internally godly manner no matter what happens. And that is another subject. 
