Bingowings said:
I always go out of my way to gently lift them off the pavement when the weather takes a sudden turn and put them onto a leaf or something
Excellent!
Sudden changes can sometimes disorient a bee, particularly if she's far from the hive. It's also possible she's just near the end of her life and unable to fly back. Either way, I applaud your kindness because I do the same - with all insects.