I would NOT look for anything older than a 2013, 1st generation iPad Air or iPad Mini 2 or 3 model.
An iPad Mini maybe better for her as it is smaller and lighter to handle.
I would really stay away from purchasing any used older iPads from any local unknown/untrusted sources, as well as any action places, like eBay and the like, as there is always high risk of getting a used iPad with Activation Lock that cannot ever be circumvented if the previous or original owner of the iPad cannot be reached after the purchase.
We all see this same scenario played out multiple times a day, here in these support communities, with many people not being able to return the device for a refund.
Amazon sells older iPad models, but sometimes, these are sold through a third party on Amazon and these maybe refurbished models that are not refurbished through Apple's own refurbishing channels.
May still be good and fine for what you need and you still have recourse for a refund if something is wrong with the device when you get it.
I would see what Apple has for discounted, refurbished iPad models on their Website, as Apple uses their own approved refurbishing sources and refurbished iPads from Apple are fully treated as a brand new device with all of the same Apple warranty options and service.
Refurbished iPad - iPad - Apple
In any event, be aware that cellular model iPads ARE going to be more expensive, no matter what.
Also, if her arthritis is that bad, she may have trouble using a touch screen device as anyone with a nerve disorder or severe enough arthritis have issues with electrical impulses in their fingers to be able to properly operate a capacitive touch screen device.
Likewise she may an issues, difficulties with using cheap, commonplace capacitive stylii you can purchase anywhere, as her fingers may not generate a strong enough electrical impulse from her fingers to transfer that impulse through a longer conductive capacitive stylus.
My own mother has this issue.
You would need to purchase a stylus that uses a battery or rechargeable battery that sends a small electrical impulse to the tip of the stylus simulating a finger touch.
These types of stylii are called “active”, battery powered stylii and use either a re[paceable AA or AAA battery or a rechargeable, lithium-ion battery.
You can find many makers of these on Amazon, as well.
You may have to setup the iPad up for her using some of the Accessibility/impairment features of an iPad.
So be aware of this, as well.
Best of Luck to You!
