Any idea what she might like?
IMO, it is popular to talk about these matches, but none are hard & fast rules. Basically, to each her own.
You might find out in the end that among the whites, 'rose' overtone is preferred (but don't tell that to whoever swears by the colder silver-white... like I do). But who'se to say that some bluish-gray ones 9Tahiti?) wouldn't look great with red hair
Besides, pink or purple Freshadama, anyone? The peach-pink pearls should look great too (remembering my red-hair days!).
It is probably easier to be daring buying for oneself. But if you did want to try something fancier than good-old-white, that's what return policies are for
My 2c
There used to be a detailed discussion about pearl overtone and user traits here. You might want to run a search.