...welcome to the world, Fire Emblem Fates.
I also think the Chrom/MaMU support is better than the Chrom/FeMU support and I'm not sure why they felt the need to make two separate ones when the MaMU one is a lot better about showing a developing friendship, but that's another issue.
story wise, like Chrom, she seems to be a different character entirely... oh, who did you put your character with? (sorry for the randomness )
Wow sorry for the wait >.<; Owain is epic only child, but brother, awkward XD I haven't played as a male character yet... been too obsessed with my current play through XD and Yarne... he has good development XD but I don't like him very much wich is weird because most girls are obsessing over him
anyways my brother and I (but mostly I) are working on an epic three arc go with the story-line, fanfiction, and he wanted to be put with Cordelia, and so we changed female Morgan's name to Phoebe C: Severa, she's so fun to write XD
I feel like I just ranted D: sorry...
But, that said, she does get up to 41 magic at a Dark Flier and 43 magic as a Sorcerer.
Now, this doesn't seem all that good, seeing that we have characters like Miriel who have +3 Magic mod and Sorcerer/Sage access (47/49 magic respectively). And of course, characters like Miriel also have Tomefaire, giving them an effective stat after its boost of 52/54 magic.
But then we should consider Cordelia's Armsthrift access.
This means that she can used Forged Tomes without burning through them nearly as quickly (not at all if she has a pair-up, rally, or other form of boost that brings her up to 50 or more luck; Limit Breaker also works to this effect if one's using the DLC, but its not necessary either).
And this also means she can make better use of un-purchaseable items with low durability, which you tend to not want to waste.
Granted, characters like Miriel can use forges and can use un-purchaseable items as well, but its quite wasteful to do so as you'll burn through resources too quickly.
So considering that Cordelia can use them without being wasteful and characters like Miriel cannot, we can assume that once she attains a regular 50+ luck after relevant bonuses that Cordelia will be using fully forged weapons all the time and can also use the un-purchaseables if she wants to.
This is particularly relevant if she goes to the Sorcerer route with "Aversa's Night".
It has 15 might, 8 more than the comparable Nosferatu tome that Sorcerers can use. And she'll likely use it fully forged while a Nosferatu user without Armsthrift isn't likely to use one that's forged, or at least not heavily forged.
So that gives her effectively 13 extra weapon might in an HP-draining tank role over another Sorcerer in many circumstances.
A Tomefaire Nosferatu Sorcerer Miriel might be able to get 59 might from 47 base magic + 5 from Tomefaire + 7 from Nosferatu.
An Armsthrift Aversa's Night Sorcerer Cordelia can get 63 might from 43 base magic + 20 from a fully forged Aversa's Night.
If you are running the DLC limit breaker on both of them, these numbers increase by 10 each, but that's an equal gain on both of them so it offers no relevant direct advantage on the Might front. But it means that Cordelia would then hit 54 luck by herself, which means she has a perfect Armsthrift rate without pair-up.
In terms of using Waste/Celica's Gale Miriel still does more damage, as she has a 9 point initial lead on Cordelia [ (3-(-1))+5 = 9] and Cordelia's forging [which she can sustain indefinitely but Miriel cannot] only accounts for 5 Might. So Miriel wins by 4 points per hit on that front.
I dunno why I really care, though, I use them both equally.