how much work was she in before the 3 months off?
I completly started again with all fitness of shay, i walked him for 12 weeks and im now only starting to trot more, and hes having a few very short canters, just to keep us both sane really. He will do trot work for another 12 weeks, increasing how long we trot for, and then progress to canter work, and then longer rides, at the moment he is only doing about 5 miles, we will be building up to 8 miles soon, im not sure of the milage of the longer rides we have, but id guess they would be about 10-12 miles, if not a bit more. My horse is being fittened for endurance work tho.
the usual fitness plan is 6 weeks with the horse being worked everyday, but you need to take into account the starting fitness of the horse, any physical problems the horse has, and somehorses can get fitter quicker than others. Because my ex racer has been at peak fitness before, she seems to get fitter more quickly than my cob, that can be taken into account, but fitness should be progressed slowly.
In 2 or 3 weeks work from being roughed off, i would expect a horse of mine to walk and give 1, maybe 2 short trots.