Figuring out the possible triggers for this systemic upset

Rolling around in my head what changed at this ride versus other rides I've been to which she presented well, no tummy troubles, no calcium issues, and good vet scores.

• Calcium:  Though I did electrolyte pre-ride, and during the ride, what I did not do is feed the handy 2 flakes of alfalfa that I've given her in the past.  Journey has mild heaves, which we've gotten totally non-symptomatic by pulling guess what? Leafy legume hays.  Leafy alfalfa can trigger it, and she will cough herself silly.  By pulling the alfalfa from her diet she has been symptom free and non-medicated for a year.  But also she would not have the calcium reserve to draw upon.   
• Beet pulp:  See above-beet pulp is chock full of vitamins and in the past I've fed it religiously.  She can be finicky about eating it and over the past year I've moved away from the beet pulp as she is 50/50 if she will eat it.   It is going to be going back into her diet.  
• Training:  I won't say "where" my job is, but the schedule change has just totally ruined my ability to train properly.  I am so pissed off...as Journey and the trail are my "good" place in life, and if I can't do that, take care of my horse, enjoy my few rides (ie: happy healthy horse) then the job frankly IS NOT WORTH IT ANYMORE.  I'm going to have to do something about that.   I've held on because I have a lot of vacation time built up to use for rides, but if I can't get a good base on her, well what is the point?  So I went to the ride rather "under conditioned" and it is bit us hard (it hurt my horse).  Though I in fact was conditioning her on hills (as I had no time to haul out to get to the flats), it did not make an equal exchange for the long trotting sessions we needed.     I'd hoped it would, but it did NOT.
• Slippery Elm:  Normally I feed some slippery elm as a stomach buffer.  It makes the gut much happier hauling.   Her gut sounds at the vet in were a B- and I've never had "that" happen before either.   

So it boils down to a lot of changes, too many changes, and my horse paid for it, and I feel like a pile of dog doo.    It was a mild tie-up as tie-ups go, but totally not acceptable.  I'm having the vet out on Friday afternoon, and we will pull blood and see if she is able to ease back into slow work.  Very much doubtful that Top of the Rock will be in the cards for us in three weeks.  If not,  we will re-group, get things back into place, spend the summer lengthening our training rides, and be fit enough late in the year to enjoy the last rides of the season as I'm a lame duck in hot weather.