Ridecamp: [RC] Shivering?

I took my mare out on a pretty long trail ride yesterday - she was bright eyed the entire time, happy, ate grass when we rested, ears up and trucking along, etc.  When we got back I hosed her off and a few minutes later noticed that she appeared to be shivering.

After a moment of panic I decided she could either actually just be shivering (it was warm out but the water was pretty cold) and/or her muscles were fatigued and the shaking was from over-use.  She was totally bright eyed and perky eared, not dehydrated, good cap refill time, CHOWING on the grass, walking fine...  When it first happened tying up was suggested but she didn't seem distressed in any way and there were no other symptoms besides the shivering.  It made me realize though that I don't know what to do for a horse that IS tying up.  :(  What do you do?

I massaged Bigeloil on her shoulders and butt muscles and tried to give her some bute in her dinner (which she passed up because she has extrasensory bute detecting skills).  She was very happily eating her hay though, drank, pooped and peed.  About 2 hours after the initial shivering she still had a little quivering going on but again everything else seemed good.  What was this?  This means I over do it with her?  Is there anything besides liniment and massage that I can do for her?

worried ...