Irises can grow flower-free for many seasons and because of many different reasons. Anything from not enough sun, planted to deeply, improperly watered, overcrowding, etc...For this particular case I would suggest that the issue may be something else. To me it sounds like a soil nutrition issue. If the leaves of her Irises were slightly yellow, I would suggest that the soil is nutrient poor. If the leaves are deep green and flourishing, I would suggest that the soil has too much nitrogen in it. Sometimes when plants have too much nitrogen available to them, they go into a vegetative state (a vegetative state means something different for plants...this means they produce new leaves and stems, but do not produce flowers). Of course there's no real way of knowing for sure unless a soil sample is sent to a soils lab for analysis. If it is assumed that too much nitrogen is the culprit for a lack of flowers, I would recommend leaching the soil and then fertilizing with a low- or no-nitrogen fertilizer. I would also recommend a fertilizer that is relatively high in phosphorus. This should induce flower initiation.
