I think it is a good move to put them out with your girls, my three have fit in really well, and I attribute that to letting everyone see them from those first early days.
Now they are running around in the barn and a bit outside like pros, they know to run and hide from the beo.... (errr I mean bully girls), and the rest just ignore them. They won't be 3 weeks old until Thursday - and it is miserably cold here but they are thriving! It's still only 6C (43F), this morning it was 4C - and they were buzzing around like crazy, when they got cold they would run under their brooder plate, but that wasn't often.
Can't wait for them to see snow tomorrow morning hahahahaha - mean Kelly!
As for your girl, I know you are more than capable of clipping a toe nail short and getting that blood sample. Just wrap her up tight in a towel and then lots of treats after... I have a lot of faith in you
(I will have to do something similar to gender test those silkie chicks, but I think I will get blood feathers instead - their toes are just soooo tiny!)