Aveline, I can relate to your friend, as that was me until 18 months ago.
I have had a degree of hearing loss all my life - when about 7 or 8 an audiologist visited our school to conduct hearing tests on the pupils, I was deemed to be high-tone deaf, possibly due to having had the erithromycin antibiotic as a small child. ( A known side effect).
It wasn’t bad enough to be a handicap to me, until my hearing deteriorated over the last decade. I’ve lived alone for the last 14 years, so no partner to converse with. I had the volume on radio and TV turned right up, and used subtitles too, so I had adapted to my hearing loss, but did have problems understanding quiet voices and mumblers.
A close friend who visits once a week occasionally mentioned I should have m hearing tested, as I often had problems with her speech - she tends to mumble, and sometimes puts her hand to her face while speaking, which could be frustrating!
I decided to bite the bullet 18 months ago, and booked a hearing test with a private audiologist, which showed that I had moderate to profound deafness (in the upper register), and I went ahead and purchased top of the range aids which were programmed to my deafness. (I bought private as I was able to afford them, rather than go through the NHS).
The effect was transformational! I hadn’t realised how many sounds I had been missing! And it was rather overwhelming for the first week or so, but I persevered by wearing them all day, and soon adapted.
I realised how much I needed them when a problem developed with them a few months ago, and had to go without for two weeks while they were checked over. They were replaced with a new pair free (being guaranteed for 5 years), and I was really happy to be able to hear again!
Mine are very discreet, almost invisible, with just a fine silver wire from the “bean” behind my ear to the receiver which goes in the canal. (I’ve attached a pic).
So, I suppose what I’m saying is, do see if you can find a tactful way of mentioning to your friend (as many have already suggested), as she would no doubt find much benefit from wearing aids.