I have to clip the feathers on my Seabright. I also had parrots years ago and we clipped their wings also. This is how we have always done it.  First thing is that it is easy to do. Does not hurt. If you trim a feather that is still growing in you may have some blood. I can not believe that would be an issue with a hen, but it can be with a parrot. But just so you know....just in case.... blood feathers will sometime keep bleeding, so either pull the feather out ( we did not pull any of our parrot feathers out) or just take a pinch of flour and then pinch the end of the feather with the flour. 
We use two people for both parrots and hens. Go out at night, pick up the hen who is flying out of your pen. Just hold her how ever it is easy for you. I hand her to my husband, and he wraps his hands around her body gently Then I gently stretch her wing out and clip the last few flight feathers, except I leave the very last one so she still look nice. I do both wings because I don't want her to still be able to fly, and with some feathers on one wing and all on the other wing she can still get over the fence.
If you find you left to many flight feathers just repeat this and trim a few more feathers. I am sure there must be lots of sites on the internet for wing clipping for parrots, most all parrot owners clip the wings. But it is very easy. The flight feathers will be the longish feathers at the end of the wing. Just cut them off even with the feathers that are on top or above them. That would be about half the feather on my seabright hen. The shaft of the feather will be dark where it has blood and the part with no blood will be more transparent.
When my kids were little my daughters helped me do our parrots, I held and they trimmed. Even with kids it was no problem. 
I am home a lot by my self, I would rather wait for a second person, but if I need to, I can clip the wings myself. You don't want to cut the hen so if you can not hold her against your body and still be able to gently stretch the wing out, and clip with the other hand try this way: take a large towel gently wrap the bird, include covering the head so she will be calm and still. Then either use a table or the ground, and gently lay the hen on her side, reach in and stretch the wing out of the towel and using your body and knees and legs to calm and steady the hen clip the feathers.
The hen will let you just  pick her up right off the roost and be sleepy and calm at night, so that's when we clip the chickens that need it. I know this is way to much info but the first time I had to clip a parrot I was very worried about exactly how to do it.