Probably.

She isn't old, even if she has lived over 10,000 years. Night Elves live a very long time and you can't judge their biology by a humans. I imagine she is closer to a mid thirties aged human than an old lady.

I would imagine that the immortality the Night Elves have enjoyed for the past 10,000 years was more the "stops your biological clock once you reach physical maturity" sort. Can you imagine the trouble that could be caused if it worked otherwise?

* If it just froze the Night Elves at their current age, you could have the elderly and children left over who were unable to pass on or grow up, respectively. And what would happen if a woman was impregnated? Would the fetus grow and be born and THEN stop aging?
* If they were immortal meaning that they were simply incapable of dying, but still aged, then you'd have a ton of ancient, incredibly decrepit night elves with no way to escape their mortal coils.
* In a similar vein, if their reproductive abilities aged normally despite their immortality, they'd be walking on a razor's edge of trying not to breed too quickly (and thus cause harm via over-population) but they'd also have to be careful not to breed too slowly! (What would happen if all existing night elves were past the age of reproduction?? Whoops! Better hold onto that immortality with both hands, otherwise you'll become extinct!)

Or they could have one of the more common fantasy elf traits which is a difficulty in conceiving.
Most elves in stories seem to have few children in addition to being long lived. All children for them are rare, but they do occur.

Though your freezing idea is also a good one. There are no children in Darnassus.

Draelan is right, altough it is kind of a mix between the "do not age past 30" and freezing. Though lore isn't exactly clear on this, this is how I see it - since planting of Nordrassil, majority of the male night elves were in a state of deep slumber, waking only in times of great need, so the birth rate was very very low, and it was balanced (in terms of total population) by accidental deaths during hunting, exploring, rock'n'roll concerts etc. There were no elderly because all of the remaining night elves (that didn't become high elves) were the younger generation. There were no older druids. The first night elf druid was Malfurion, so every other nelf druid is of his age or younger. And since all the older males died or became high elves and females probably stuck to their partners, so they were of similiar age (no cougars in night elf society, apart from the druid forms :-D), no older females either.

Think that Malfurion spent most of those 10,000 years either battling ancient evils in the other side of the continent or asleep (well, not asleep asleep, but roaming in the emerald dream. And I remember reading that high elves seldom had any children, probably from Night of the dragon, so I assume Night elves might as well.