@FatFilledTrottyPuss I'm very envious of the lovely views from your window!
OP, it's important to be able to thoroughly clean bird feeders on a regular basis, to avoid the spread of diease. So, look for feeders that are easy to dismantle and reassemble, and make sure thy're not so high that she can't reach them to clean them and refill. Also, avoid getting extra long feeders with the intention that they will last longer between refills - they may do, but if food is hanging aroiund for too long, especially if its damp from the rain, mould and bacteria will grow. I find the clear perspex feeders with holes/perches near the bottom and a little roof to keep the contents dry are good. Get her one or two more feeders than she has hooks for - that way, one can be washed, dried and ready for use, as soon as the next one is empty and awaiting washing.
We have a tall "shepherd crook" style bird table, with several hooks for hanging feeders. It has a pointy spike which is sunk into the grass and this keeps it sturdy. We have a clear acrylic "squirrel baffle" which is a hemisphere of clear plastic which is mounted on to the pole of the bird table, about one metre from the ground, and it stops squirrels/rats from either climbing the pole or jumping onto the feeders. Try to avoid rustic wooden feeding tables with lots of nooks and crannies where food gets trapped and goes off. They are very difficult to clean properly.
Different foods will attract different birds but I think my most popular feeders contain suet balls, sunflower seeds (especially hulled) or niger seeds.
Be careful about ground feeding tables - they seem to attract rats, in my experience.
Birds need water even more than food, especially in winter when their usual puddles and ponds may be frozen. Again, bird baths/water bowls must be cleaned regularly. DON'T put antifreeze in their water (I'm sure you wouldn't, but some people do). It kills the birds. Bird baths/water bowls should be shallow, with a rim they can cling to. Don't place in bushes or the shrubbery, as it allows cats and other predators to sneak up on unsuspecting birds as they splash around, and catch them.
I hope your mum enjoys watching the birds. They can be very entertaining.