Congratulations on the two calves
How are the cows with you, have you been up close yet? If they are very quiet, as Herefords often are, maybe try stroking the udder in the field and see what reaction you get.
Personally I wouldn't want to stress a new mum if it's avoidable, but if you are still keen to explore the idea of milking, there would be no harm in just taking it easy step by easy step and stopping if she seems to be becoming agitated.
With a heifer, especially of a non-dairy breed, it's best done as soon as possible. In my experience, the longer she is left as a suckler cow the more "my milk, my calf, my teats" she will become.