Check out the current Siromer models. They are small, reliable tractors with simple controls. I'm older than your Mum and I love ours, which was one of the first Siromers imported into the UK. They are, or were, much cheaper than the British equivalent, the choice depends on how much you want to support the UK at your own expense. We have implements for our Siromer - a front loader with both forks and a bucket, but changing them over will not be a job for your Mum, a small plough, topper, rotavator, rear hydraulic arm for attachments such as a hedge trimmer, spring tine rake and a roller. Not all the implements are Siromer brand as other small tractor stuff fits fine and tends to be cheaper - perhaps the importer makes his money from the add-ons. We also use a small trailer with ours. I definitely have trouble with changing implements on the 3 point linkage as my hands are arthritic but perhaps your Mum doesn't have that problem.
We also have an ancient David Brown for heavy stuff, which was a gift, but you won't need anything like that - you should be able to do all you need to with the Siromer or a similarly sized tractor. Sorry I don't know how much they cost now, but worth including in the suggestions you consider. btw, spares for Chinese tractors cost a lot and take a while to arrive, especially when they come via the Suez canal and some big ship gets stuck in it, but locally available 'pattern' spares are loads cheaper by mail order.
You didn't say if you want new or second hand. Both can be reliable, or both can be a nightmare with breakdowns just when you haven't the time for that. Older models are likely to be a bigger problem and unless you have mechanical ability, steer clear of very old machines like the Little Grey Fergie - romantic but can be a pita.