Imac spec for AE

if it were Blender or something, that would be a good start for someone just figuring stuff out for a bit, but for the most part, macs, while advertised to be "creative-orianted" are generally behind the curve, even when it comes to new ones. Consider a mac to have 1-3 years less longevity in future-proofing, and the fancy cases usually have thermal issues which cause them to become unreliable for rendering, mid-task.

I find that, as opposed to other programs, as well, After Effects sucks up resources for no good reason. it WILL max out your RAM every time it can, and then begin using your disk to store the excess. This is basically abuse to older drives, and will shorten their lifespan. At the very least I suggest getting a new drive, which on apple hardware... may or may not even be possible. apple wants you to buy a new one after all.
I consider Imacs just like laptops, with a different form factor. more powerful, yes, but overall the aesthetics get in the way of making them proper workstations. 
and yes. I learned a lot of video editing on the exact computer you're talking about.
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I assume you're buying it used. You wouldn't be considering this if it was a hand-me-down. Given the current going price of $400-$500 for a guaranteed working or refurbished one, I'll get you some parts that'll make a real fancy one for the same price.-
you can do MUCH better with last gen (but not quite 9 year old) parts if you build your own. Adobe software doesn't generally use GPU's. That's a HUGE money saver, but chances are something she'll do will require one.

https://pcpartpicker.com/user/nubnubbud/saved/#view=vNQGkL 
This baby punches WAY above its weight class. it's twice as fast as my 2017 budget workstation, at least for adobe products. Most of the price reduction comes from not having a discrete GPU, but Adobe products don't generally use one. Its integrated GPU is one of the best in the industry and even usable for light gaming. 6 instead of more cores let it take advantage of Adobe products' need for higher clock speeds(it's a choose one or the other thing. more cores do lots of simple instructions, faster cores do more complex ones better), and a good chunk of the price comes from the RAM. 64GB is considered the minimum for a professional workflow, but you can halve it if you're still learning and get pretty good performance for smaller or simpler scenes. Oh and it has gigabit wifi. just in case.

the only downside is you'll have to scrounge around for a monitor to use it with. Keep in mind all the computer manufacturers switched to a new socket earlier this year, so the upgrade path is "get a new computer after a few years".

https://pcpartpicker.com/user/nubnubbud/saved/#view=mJ8jGX
this is the exact same, minus some bells and whistles like a more beginner friendly case, a little less RAM, and less storage.
At this point you're scraping the bottom of the barrel for savings. It'll be more than twice as fast as that Imac, even in this config, but we're getting it so cheap, that upgrading it with any more storage, usually the cheapest funcitonal part, will inflate its price more than 20%. Also this one comes with RGB lighting. yipee?

There's a reason so many editors make their own computers. strong editing computers have different needs than gaming computers, and prebuilts, especially workstations, come with a massive luxury tax. building it yourself is a nice project, something to do with your family if it's a gift, reduces prices often by 30% or more, you'll know how to fix and upgrade it-
and it's undeniable that if you built it yourself, it feels a little more special than just a tool.

Are you seeing any used 2017 models that fit your budget?  The main challenge of a 2014 iMac is that macOS will not upgrade past macOS 11 Big Sur.  While you can run After Effects 2023 now, you may not be able to run anything newer as it's released.  If going used, I'd look for a 2017.  

I used to work on a 2013 27-inch iMac.  It handles 1080p in Premere Pro and After Effects really well (especially ProRes based projects) and also runs Photoshop, Illustrator, InDesign, and Audition well.

Not really. At this point support for intel-based Macs is already bad and it soon enough will be non-existent, both on Adobe's end as well as Apple's. Those old iMacs have tons of bugs and issues. Whatever money you plan on spending on this, even if it's just 300 bucks, would be better allocated to funding a cheap PC-based laptop or similar.

Mylenium