Very wet hen

One of my hens is suffering with saturated feathers after rain. The others are fine, they all have the same feed etc but this one has been very ill (nearly died in fact) and her feathers really lost their condition. She is already showing signs of having a cold (sneezing - at least that's what I think the little noises are) after a drenching a 2 or 3 days ago.

Is there anything I can do to help keep her dry?  I'm going to bring her in and hair dry her, but what about spraying her with olive oil? Any thoughts?

They are free range (over three acres) with access to shelter but she gets soaked at the first few drops of rain.

Thanks in advance for any help!

Thanks Ghost, she's actually been much better e.g. Drier, each day since I posted this question and we've had quite a bit of rain, so I think her condition is returning. She's certainly preening properly which must help.
I actually left the door to the polytunnel open by mistake on Saturday lunchtime (it was pouring down up here) and only remembered in the late afternoon. I went tearing up and found all six hens sleeping inside but on the old carpet we have by the door. Little chick was lovely and dry as you might imagine!