Well the surest sign would have been if she had come back into season, if she didn't she is most likely in-kid - I would think. Is she a goatling/first kidder? If yes, I would think the udder would start to develop around now, it is not always possible to tell from their shape that they are in kid, especially if it is only a single in there (My 1st kidder BT looked fairly neat and dropped triplets

).
Her tailbone will also move up a bit, but some goats only start this very late on, others do it for weeks beforehand, so not a safe indicator.
I would increase her feed ration a bit now, although if she is out on fresh grass maybe not needed too much (mine never kid this late), and watch that she keeps eating some concentrate (pregnancy toxaemia). I would also give her a booster clostridial vaccine about 3 weeks before the expected due date, just to be on the safe side.
However if she goes past her due date I would start milking her out after a week late, if she is from high-yielding stock she may well be a maiden milker (although if she has been to see the billy and he most likely did some sort of business, not sure she would be a "maiden" anymore, but I leave that discussion to others...

)
She may just surprise you! (Please keep us posted!)