OP I had both eyes done at the same time and was sat in a chair like a dentist's chair. It was reclined a little bit but I felt like I was sitting in it, not lying back. I went privately as I had implanted multifocal contact lenses which aren't offered by the NHS so it might be a slightly different experience. Regardless of that the staff will be very used to nervous patients and will help her through it.
Firstly I had two lots of anaesthetic drops in each eye, 15 minutes apart I think. I was sceptical that they work, we're used to oral or injections aren't we, but the first lot felt cold and the second I couldn't tell, so knew they were working. I had to alert the surgeon that I could feel something as he started the second eye, but it wasn't painful. He put more drops in and it was fine., so tell your Mum to speak up if she feels the need, or even if she needs reassurance. There was absolutely no pain at all despite all my fears, possibly just a mild pulling sensation in one eye. The strange thing was that despite one eye being covered, I could still 'see' through the operation, nothing horrible, just very pretty colours and shapes. That was a surprise. I was in the theatre about half an hour in total.
Because I'd had both done I didn't have a shield and I walked out into a world brighter and clearer than I've ever seen. I could read within hours too.
My eyes did feel dry and gritty for a few days, a bit overly tired if you like and I couldn't go without some good wrap around sunglasses. Screen, TV and reading time has to be limited at first and the post op drops used diligently. She should increase hand washing and avoid touching her eyes over the days afterwards to make sure she doesn't pick up any infection.
I'd say the most difficult thing about it all was the unnecessary worry beforehand, hair washing afterwards and remembering not to bend or lift things, basically do nothing that adds to pressure on the eye. Your DM's friend is vastly over egging the pudding and her comment is mean. I tell you honestly I've had more painful beauty treatments and besides that the benefit afterwards is amazing.