Many planning departments are very subject to being swayed by the individual views of the planners. I doubt that the development plan contains a specific ban on two story houses in your area. Rather, it is more likely to be the individual planner's interpretation of the aspirational language in the Plan. Most planning officials don't stay put in one area for more than a year or two -even if staying with the same planning authority, they might be responsible for a different area within the county.
If this lady's views are incompatible with your proposals, if you sense that there is no give in her, and if you are not in a hurry, it might be worth while adopting a "wait and see" attitude for a year or two, as there is a good prospect that she might move on. Alternatively, you could simply put in your plans and see what happens, but a planning refusal tends to follow a site: if she refuses two storeys (and An Bord Pleanala follow suit) the chances of ever getting two stories on a subsequent application are hugely diminished.