Yeah they suck all the work Tanya did and they give her so little trust not even ask her explain herselves over channels. Just because they are afraid of taking responibilty if things go wrong.
It was a direct order. She obeys them. If it had been something more like 'A Ceasefire will be announced' she could've started before receiving that order and then claim she hadn't been ordered yet.
Or if they had said something like 'A courier will arrive with further instructions' and then sent Lehrgen with any vehicle, she could've acted before he arrived.
That being said, we're not entirely sure what level of communication technology they're at ? Strictly telegraphs and radios ? It could take too long to even get in touch with Zettour through all the levels inbetween them, and then trying to convince the duo over radio of something that ludicruous to them ?
I mean, they're trusting her a lot, but that and being convinced by something like this which is a first for this world through radio and with a tight time schedule which the mere act of communication might overshoot ?