Internal wall so damp paint won't dry

[WhyCantPeopleBeNice]

Can anyone offer advice on what to do.
I've painted my daughter's room this weekend.
We've sanded the whole room as part of the prep and didn't notice feel any wettness at all.
Painted the first and second coat on a wall to make sure she liked it which dried fine, so not a paint issue
Then painted the next 3 walls, 2 are external walls, one has the window.
The window wall is totally wet, 6 hours later the paint hasn't even started to dry and in places is running off the wall. This is the same for about a foot either side of the wall.

Top and bottom - the whole wall is equally wet yet, as I said, when we sanded the walls there was zero signs of any issues.

I don't know where to begin even working out what's caused it to stop it/dry it?
Do we wipe off all the paint?

I’d wipe it off yes, but it Could be anything from over full gutters on. Either way she cannot sleep in there it’s a health hazard.

Do you have your heating on? The wall might be damp because it's so cold and the external wall is wet from condensation.
The paint will be adding extra humidity into the room.
You might find it is dries fine when the weather warms up.

@Swimmingpoolsally fear not she's decamped to my office already due to the dust from sanding and paint smells.

The heating has broken, but we've got the fire on which is usually sufficient to heat the whole bungalow and all internal doors have been opened, we've also added the small electric heater which has been going each time the room temp drops

I'll have to check gutters tomorrow

This happened at my old house. There was no insulation in the walls at all because it was such an old house and it was constantly damp around most of the house. I got a dehumidifier because after 3 days my walls still had soaking wet paint. This helped to dry it for the time being but we ended up needing to get the walls insulated.

It's super cold right now, that's why & there'll be internal fine condensation on those outer walls that won't be helping. Ideally the room would be 21C (standard room temp) to dry out very well.