As a guy that works at a repair store, used laptops are insanely cheap. You’ll get a much more powerful and capable laptop if you go used, and you’re not at any risk because many reputable sellers and refurbishers will provide warranties too.
Most importantly when looking on eBay for laptops you want an SSD, if it says it’s using an HDD or “hard drive” avoid it. SSDs are 6x faster or more than HDDs and are much more reliable in mobile devices. They are cheap now too and most quality refurbs will have an SSD in most of their devices.
A lot of SSDs are somewhat low capacity so make sure she gets a little more storage than what she needs right now, but also external storage is pretty effective if the laptop’s storage gets a little full.
Other important features. 1080 HD screen. This will be really nice to have and often means that the processor on the laptop is pretty decent too for day to day tasks (most modern CPUs on many computers are far more powerful than most people ever need).
8gb or preferably 16gb of RAM. A lot of new computers today have a lot of RAM, which now means software devs are a lot lazier optimizing their programs. More RAM nowadays is really important and for good longevity I highly recommend 16gb.
Availability of parts. If you’re interested in a laptop, open a new eBay tab and put in “laptop model number parts”. If you see an abundance of cheap parts available that’s a very good sign. This means repairs are not only possible but likely easy and cheap.
Additionally feel free to ask questions, if you see a laptop that’s great but lacks a bit of ram, or has an SSD a little too small you can ask the seller to upgrade it. It’s gonna cost a little but shouldn’t be much. Unfortunately screens and processors (in most cases!) cannot be upgraded and usually not worth asking.