I have been giving further thoughts to your auntie´s problem over my breakfast.
I assume that she has had a hearing test (audiogram) and I assume that her hearing loss is in the high tones, the low tones being acceptable.
An NHS aid will amplify ALL sounds, high and low as explained by Buenchico and with an NHS aid, you will never hear normally and you must accept that fact.
Now go back to the Audiology Dept and ask then to check the mould in your ear and also the fitting.....ask them if they will make a mould for the opposite ear and try the aid in that ear.
If all this fails, then go to Boots and ask them if you can have a free trial of their private hearing aids, which are more cheaper than "Hidden Hearing"