Are you thinking Oak Leaf Hydrangea? Or, you already have it? 😱 It will eventually - or maybe sooner - make your fence collapse. Clematis much safer bet - many mature sizes to choose from. They bloom sooner & in many colors. Encourage your daughter to do a bit of research.. Ask her where she saw it & what the conditions were for it.

It all depend on the size of the wall that you are talking about. Climbing Hydrangea can exceed 80 feet log.

Oakleaf hydrangeas don't climb so I suspect this is not the plant in question :-) H. anomola ssp. petiolaris does and can, as luis indicates, grow to a considerable size. But with care and proper attention to pruning, it can be kept significantly smaller. I inherited one in my current garden that grows and blooms quite happily on a small section of 4' tall chain link fence. Other than some occasional pruning to keep some wayward, outward reaching stems in check (it borders the road and parking area) it gets no further attention.

But I tend to agree that a hydrangea may not be the best choice for your situation. They can take a substantial amount of time to establish and start blooming (5-7 years or more), the bloom period is quite short - only a couple of weeks - but they do hold the spent flowerheads well to extend the season of interest. And any pruning considered to keep the plant smaller must be done selectively and carefully so as not to remove the old wood flowering potential.

Clematis may indeed be a better choice. A wide range of sizes and colors, there is one to fit almost any gardening situation. And they bloom sooner, heavier and longer than the hydrangea would..