5 Answers

The problem may be  the cow needs to be in isolation and they've nowhere else to put her. Have you called and expressed honest concern?  "I noticed one of your beautiful dairy cows has been separated from the herd.  Is she ill?"
OR, you could contact the local SPCA and have them find out what is going on.  
 

I have never owned a cow although I would like to as I adore them... Here are some sites that I have found...

http://www.justanswer.com/sip/Cattle/Large%20Animal%20Veterinary?r=ppc|ga|2|Pets+%2D+Large+Animals|Cattle&JPKW=cattle%20health%20problems&JPDC=S&JPST=&JPAD=11105425978&JPMT=b&JPNW=g&JPAF=txt&JPCD=20120207&JPRC=1&JPOP=Darren_Andrew9sec_Trans&gclid=CK7klY7gma8CFWUaQgodviP7ag

http://animalscience.tamu.edu/images/pdf/beef/beef-common-health-problems-beef-cattle.pdf

http://www.dpi.nsw.gov.au/agriculture/livestock/health/specific/cattle

I hope this helps.

I don't know anything about cows, perhaps she is just old (?) but I think I would have to ask if there were anything I could do to help, that way you would at least know

The poor dear!  If she truly is lame or doesn't rejoin the herd in a few day I would ask around to see if anyone knows what is going on.  Could she be pregnant?

At this point (4 mo. after question), I doubt that the cow is still in the yard!  If so, is she still alive?  It is not uncommon for farmers to have an animal who is a downer, and they provide supportive therapy for them, away from the other animals who would harm them.  It does not mean that they are being cruel to the animal!  The animal may be pregnant, as one had suggested, as a matter of fact, Dairy cows must be pregnant or they are not able to produce a constant flow of milk, meaning they must have a calf each year, with a "dry period" just before calving.  This is when they are not milking, but they begin milking after the delivery of the next calf.  Sometimes they get an imbalance of Calcium called "milk fever" and this animal could have this, treated with an injection of Calcium into their bloodstream.  It acts quickly, and they stand right up, so this probably isn't the problem.  She could have bad feet, and it could hurt her to stand, or maybe she is an older cow, in her dry period, and is just lounging around away from the herd, finishing her gestation, awaiting her next calf delivery.  Or maybe just plain waiting for the meat truck to pick her up and take her to slaughter, that happens!  Where do you think hamburg comes from, not McDonalds'!!!