I have put heifer calves back in with bred cows after 8 weeks of fence line weaning with no problems. I recall seeing a calf trying to nurse her dam when I first put them back together. The dam gave her a little kick and that was the end of that.

I was limited for space and had no other option at the time for retained heifer calves. This was a couple years ago and NONE of my heifers or cows suck on each other.

If a cow or heifer is sucking on another after weaning I look at it also as the fault of the cow. A good mothering cow usually won't let another suck on her when wet.  My cows are generally pretty well past the swelling and dried off after 8 or 10 weeks.

Fwiw

Jim