Argos

Kind of understand your frustration, with a family member in hospital.

But, on the Argos website, its policy is clearly laid out on returns.
All sounds reasonable to me.
You cannot just replace it if having tried it and it does not fit your needs. With Argos obviously not seeing/trying the goods has always been a known problem to consider.
It is so easy these days to go on YouTube and see a review of any tech or that matter visit a Currys or John Lewis and have a play before purchase. Something I will always do with tech to get a full lowdown.
Mind, you may not have been able to fully to do that with your family member eyesight concerns.

If you've changed your mind and need to return an item, you have 30 days from the date of purchase or date of receipt if delivered, to return your item(s).
Your item(s) needs to be:
Unused and with all original components
In its original packaging (with the tags if applicable)
In a resaleable condition
With its proof of purchase
With any free items that came with the product
Refunds will be processed by the original payment method. If you paid by card, it can take up to 5 working days to appear back in your account; with PayPal, refunds can take up to 30 days.

https://www.argos.co.uk/help/returns-and-refunds/

Argos are usually quite good in their stores, so maybe try another store or I have always found their Live chat team to be very good, maybe worth a try and see if they can offer a more sympathetic tone.
https://www.argos.co.uk/help/contact-us/

Sorry to hear about your mum Jezza.  The live chat option might well be best.  You usually get someone more customer services focussed and willing to go the extra mile.

How about activating voice response on the tablet so your mum doesn't have to mess about with buttons?  There is a short video here about how to do it on the tablet you have bought.

https://www.youtube.com/watch?v=xRXJcOMB_zg

Can you 'bigger' the icons, Jezza? Can't help there, but maybe there's a way!

As said by chums here, try the Chat; you have a good case for a return, as £160.00 is not to be sniffed at! I've found Argos are pretty fair on returns, but may need a nudge occasionally...

Ebay show several at nearly this price, so you could sell it on, but there again, I don't know the specification you have on your Mum's.

Tell her we're on the case - it might make her feel better anyway! We hope so!