Either find a calf to graft on her and salvage the lactation; or let her dry up and sell her. Bred cows are fairly cheap, so you cannot justify keeping her, rebreeding her and waiting for another calf that as stated by @Lazy M, you won't be selling for at least 18 to 24 months from now. The sad thing is, buying her late trimester, close to calving, she may not have gotten enough decent feed and the calf just didn't have the nutrition in the womb, to thrive when it was born. Not really her fault, but bred cows are just too cheap to justify putting much into her. I'd be putting a calf on her if she was mine, then letting her raise it, get bred back and go from there.
Her colostrum may not have had any "oomp" to it. Have seen it in dairy cattle, they used to test the colostrum with a meter, and some just didn't have any good anti-bodies in it. But the calf may just not have had much of a chance if he'd been malnourished in utero.