I thought of this also. We had a situation where a longhorn bull got a round bale feeder stuck on his head - no idea how he got them horns in there cause we had to trim one of them to get it off. Anyway, no one could get near him, he was pissed and slinging this large piece of steal all around and tearing things up. The vet came with a dart gun and put him to sleep. We trimmed about an inch off one horn and got the feeder off. It was quite the deal but in your situation, you would then be trying to load a docile cow that is going to lay down until the drugs wear off.Tranquilizer dart is necessary for this project.
I would find some corral panels and set them up in the shade with some water and grain and bait them in. May take several days of "gaining their trust" so they wont run out when they see you.
Otherwise maybe the vet could use a dart with a "light" dose so she wont want to lay down then lead her into a trailer with a rope.