There are some great suggestions here. Another one - great or not; more to choose from is a good thing, IMO - is to come up with a new PrC (yeah, this idea is quite a bit like Will's.)

You might or might not be aware that the 3.5 DMG encourages DMs to do exactly that, but it's true anyway. So how about it? Her character is about the right level for your typical prestige class prereqs anyway, so why not.
I don't know much about the character or the setting, but hey, you do! Therefore, I'm sure there's some way of tying this into both.
You could afford to be fairly generous with the mechanics of it, IMO, because - as Jeff mentioned - dual casters in 3.5 tend to get a pretty bad deal, all 'round. There's the Mystic Theurge in the DMG, I suppose, as a kind of template. But then, you're not gaining as much from casting Wizard and Bard spells in the first place (as Cleric and Wizard, say) so adding in some tasty extras would be totally fine. Medium BAB and d6 HP even, perhaps, just for example. Bardic Knowledge seems a perfect fit. And so on.
Or, you could discuss it together, and see what features of each class are important to her. I'm guessing spellcasting for Wizard

, but wno knows for the Bard stuff.
You / you and your player get the advantage of being able to add in world details this way, to her character class itself.
Just a thought.