Depends on alot of factors.
How much coat does the horse have? A hairy horse is going to dry much slower and could get chill from being wet too long. But a horse with very light coat isn't going to have as much protection from the chill in the first place.
Do you have a cooler to keep on the horse and time to wait for the horse to dry before removing it?
Is the horse kept outside, in a drafty barn, or in a heated barn? If the horse is outside, is it cloudy and windy or sunny?
Do you have hot water or just cold water?
If you can give the horse a bath with warm water, cover them with a cooler afterwards and keep them in a warm, undrafty area until they are dry, then it should be ok. Otherwise I wouldn't.
I just look at it this way. I don't bathe my horse in any temperature I wouldn't be ok taking a shower in myself! I'm sure the horse doesn't appreciate it
I would suggest hosing off her legs (since ice water is fine, actually good for their legs), then rubbing off any saddle marks with a damp sponge, and if its cool, throw on a cooler for a bit til they dry.