Possible Staph A or E.coli infection
This sounds like a bad Staph A or E.coli infection and could result in a lost quarter and in some cases loss of life ! I say this but without actually being there it is so hard to diagnose correctly.
You really need to call your vet who will hopefully put your cow on a 'drip' to try and remove all the toxins and fill her full of antibiotics for any secondary infections.
She will need her temp taking asap, is there any chance you could post back and let us know what it is please ? Is she scouring, drinking fluids and eating ?
She may go down if very ill so will need watching over the next 24 hours.
Good luck !