I would strongly recommend NOT to get the old MBP with spinning hdd. Look instead for a MBA 13" - it will be faster, lighter (no boat anchor) and bring her into the 21st century. The only way I'd get anything with a hdd in it, would be if it was a Fusion Drive, where you're getting the speed of ssd, the capacity of hdd and a price somewhere in between, but that's a moot point given they're not offering FD on any laptops (our work iMac has one and I love not having to think about saving anything).
For a similar price, getting an rMBP 13" would be an almost even trade-off, where you get the nicer screen, but performance-wise it will be similar to the MBA. The MBA is fantastic on battery life too - almost like an iPad where you can go 12+ hours on a charge. The '13 rMBP 15" I'm typing on now, running Yosemite, is hitting a little over 8 hours of mixed usage per charge, which is fantastic, but going all day and into the night with the MBA - is hard to beat.\
Check out Apple's refurb store to see what they offer. You can find great deals and you get all the perks of buying new, at generally a significant savings. It might not be the newest model (although you can find them too), but if she's doing work on it, what does it matter if it's a 2013 or 2014.