Trained vs. Over-trained

I've spent the past two weeks mixing some intervals into our training loop. Poor little Journey just hit the proverbial brick wall when we added a dose of cantering into the mix.  She was good the first day, maybe better the second.  She had a day off, and we went at it again, and BLAM.  Horse has 'nothing.  She is as juiced out as double squeezed orange.  So there is little doubt where the hole is in her program.  Cardio fitness (anerobic training).  Of course I know the importance of this, but have had to train the horse on many remedial levels, working out equipment, and get the LSD under her.  We also hit our worming rotation, and this put her slightly off her feed for the past two days.  Couple those with the heat wave, and I haven't had a horse to speak of.  All things considered it was time to just back off, and let the horse be a horse for a few days.  I'm going to put her into the barn tonight, stoke her up with some beet pulp mash, a half dose of electrolytes, and a pile of her favorite hay; then let her get a good night of sleep before heading out for the next few days.   So glad the temperature is dropping, now if we can just dodge the rain.