Thanks much. I clearly need to look more closely at it. I'll mention your observations and see if she still wants to take the class.
To build on what Korimyr said:
Basically, it loses the bardic combat and bardic music abilities for something of the Sorcerer's casting - there's a few things of note, though:
1) While it gets 9th level spells, it gets them a level behind the Sorcerer (you can't take the first class level until after you're at 10th, and you can't get 9th level spells until the 9th level of the class, so you're 19th when you get your first 9th level spell this way). The Sorcerer or Wizard will beat it in straight-up spellcasting.
2) The spells-per-day are still on par with the bard - at 10th level, you've got... 2 9th level spells per day (plus one from a Charisma bonus if you've gotten Charisma up to 28 by then; +2 if you've gotten your Charisma up to 36, but how likely is that?), and 2 9th level spells known. The PrC has fairly severe endurance issues, if you you try to play it like a Sorcerer.
When it gets strong is when used in conjunction with other PrC's - especially the dual-advancement ones, and other quick-access PrC's with their own lists; the Human Savage Bard-5/Ur-Priest-2/Mystic Theurge-(Bard/Ur-Priest)-3/Sublime Chord-1/Mystic Theurge-4-8 (Ur-Priest/Sublime Chord)/Abjurant Champion-4 (Sublime Chord) is quite the caster - two 9th level Arcane spells, plus a few Divine spells, a Sublime Chord caster level of 18 (depending a little on your reading of things), and an Ur-Priest caster level of either 13 or 19 (depending a lot on your reading of things). Plus a fair number of class features. There's an Exalted equivalent - the Bard-7/Apostle of Peace-2/Mystic Theurge(Bard/Apostle of Peace)-1/Sublime Chord-1/Mystic Theurge (Sublime Chord/Apostle of Peace)-X.
Basically, the PrC is fine, balance-wise, in isolation (Bard-10/Sublime Chord-10). You end up with a more skillful, moderately more durable Sorcerer that is lacking endurance and is level behind on spells. It's when you stack it with other stuff that it gets dicey.