In the first place, there's little reason to think that the bhikkhuni order was going against social norms. There are some examples of female wanderers in the Nikayas, and we know the Jains allowed nuns as well. So it doesn't make sense to presume social stigma.
This also goes to the allegations of security; the Vinaya does dictate traveling in pairs, and other rules ward against the possibilities of gossip. When comparing the Theri- and Thera-gathas, you will note that most of the forest imagery comes from the anchoretic bhikkhus, while bhikkhunis were perhaps more likely to live as cenobites in small huts. Protections could be secured, nevertheless.
So the Buddha probably said, "Come, nun" at first, just as with monks - this is, in fact, recorded in passing somewhere in the Vinaya, or perhaps in the Therigatha.
In any event, these pieces of evidence are strong largely because they are in passing; the presence of female ascetics of various kinds alongside Buddhist nuns was accepted and taking as a matter of course. It is only later that we can see a concerted effort to denigrate nuns' achievements, impose the garudhammas, and so forth.
The advice to Ananda is a case in point; 'be mindful' is sound Dhamma, and elsewhere the Buddha describes metta, and so forth, as appropriate approaches. There is an occasional suggestion that thinking of women in terms of 'sister', 'mother', 'daughter' is of use, but in these contexts clear mindfulness is always held up as the ideal. So the advice to Ananda referred to earlier really starts to look like the hand of an editor - it sticks out against the rest of the Dhamma like a sore thumb.
It's helpful, especially in connection with modern issues such as this, to take a soft and wide gaze at the Nikayas in order to discern the regularity of the Teaching, rather than trying to pierce the meaning through tiddles and jots.