Hi, I'm Dr. Bonk. First of all, I'm happy to hear that your horse is doing much better. Now, it's not very common for a horse to run a fever with colic. The temperature may be elevated, but that is usually due to them rolling, or excess kicking at their stomach. Usually these horses are drenched in sweat, so you can tell they have been exerting themselves.
Colitis is almost always accompanied by horrible diarrhea.
Fevers are common with infections. Some infections won't have any other outward signs other than the horse feeling 'off'. You can't say for sure that this was your horse's problem without difinitive testing, but given the time of year and her response to antibiotics, an infection seems more likely.
However, with a sick horse, it sure doesn't hurt to tube and clean out the GI tract to help prevent a colic episode, so I don't think the treatment or blood work hurt her in any way.
Again, I'm happy to hear that your horse is doing well.
I hope this helps. Please contact me with any further questions. Thank you!