Golden Comet Hen Lethargic & Throwing Up

[Rrwky]

I have three adult Rhode Island Red hens and one Golden Comet hen from a previous flock. The other day, I let them out, and I picked up the Golden Comet (the calmer of the bunch). She threw up water. I thought maybe I'd scared her or squeezed her crop, but I was pretty careful in picking her up. She threw up twice while I held her, so I set her down. Yesterday, she still seemed out of it. Very lethargic, not fleeing from my hand at all when I'd reach in the coop (she usually at least moves to get away). The other three are perky and talkative as ever, and she just stands there next to the waterer but this morning I stood there and watched when I put in fresh water, and she didn't drink. She just started rolling her head from side to side. Eyes half closed. So my stepdad picked her up gently to check her, and she threw up again.

My guess is she's about four or five years old, much older than the Reds. I don't know if she's sick or dying or any danger of infection to the other hens.

I am going to add some Sav-A-Chick Electrolyte to the water today, but I haven't seen her drink, so I don't know if she'll get it. Maybe she's just old? She's my favorite hen and I don't want to lose her, but I don't know if I need to separate her or spare her any suffering, or if there's something I can do to help her recover.

I am far from being a chicken expert and have no experience with sick chickens, so any help would be very much appreciated!

Thanks.