Honestly, grab a used 5d or 5dmk2. The first is half the cost of the second, and both are great at what they do. Selling the 24-105 is a bad idea unless you're planning to add in a 40mm/50mm/85mm lenses to your collection, and your has stated her preference for zooms.
No need to break the bank, just keep shooting.
Thanks for your response. I did consider the 5Dii. To me camera bodies lose their value very quickly and the 5dii is a great tool. Are you just a FF shooter in general or do you have a specific reason for a 5Dii? Wouldn't the AF system and the better low light capabilities justify the difference in cost to the 5Diii?
I'd actually lean on the 6D for the low light and AF system more so than a 5Dmk2, but for landscapes or portraits it's a solid either option works great. I shoot full frame, and would also put out there a 1Ds mk2 as an option at 16.7mp since they're under $1k used, but since there isn't a green square mode to start in, it really comes down to what you want to shoot. If you're ok with handing her the 6D, then shop for what you want. If you want to hold the 6D, get her set with something that will allow her to improve her skills without breaking the bank. How does the 6D feel in your hand, in her hands and have either of you held a 5D/5D mk2?
I'd say FF over crop based on what you shoot, so it comes down to price point: $2k for a new USA 6D, $1,519 for a refurb 6D, ~$1,200 for a used 5d mk2, ~$1k for a 1Ds mk2, ~$550 for a used 5D. http://shop.usa.canon.com/shop/en/catalog/cameras/refurbished-eos-digital-slr-cameras