Trouble is this isn't a one-off event - the OP is going to have to catch this ewe every day until her wool has regrown. So learning how to bring her in calmly so she isn't spooked will give best results. I agree with the funnel method, but it's best if she walks in, not gets chased. Sheep are not daft and chasing her around will only make her wilder to catch each time. Making a pen on the other side of the gate can work, if it's a gate she's used to going through.
If you can bring all four together, even though it's only one you want to treat, that will make the target ewe feel less vulnerable.
One trick, if the other sheep are calmer and happy to be penned, is to build a pen like a Larsen trap, with two sections. Get the other sheep in, put a hurdle across so she can see them but they can't get out, then with patience she will join them.
Once they are in and the work is done, give them all a treat.
In the long term, get the flock used to going into a pen to be fed in the winter, so they are really calm and you can quietly close the pen across when you need them.