Both hydrangea paniculata Limelight and hydrangea arborescens Incrediball bloom on current seasons growth making it possible to prune severely and still have flowers produced same year.

Having said that, younger plants - while not harmed - normally may not need that much pruning, and I wait until late winter/early spring in my zone and prune to a pair of strong buds after those buds begin to swell.

LOL!! Do we detect a note of panic? :-)

Not to worry...what appears to be a 'butchering' now will be long forgotten next season. As morz8 notes, both of these hydrangeas will tolerate hard pruning and cutting back by 1/3 to 1/2 often results in stockier plants with stronger stems. And will NOT affect flowering.

About the only 'wrong' time to prune these is after they have set flower buds in mid/late spring, but I'd save the bulk of my pruning for late winter/early spring also.

Does your mom tend to be heavy handed with pruners? Some folks have a need to conquer or tame all trees and shrubs in their care by heavy or too frequent pruning. In most cases, it is not necessary and can sometimes (but not in this case) be detrimental to the plant's health. You might suggest to her to go easy in the future :-)