MSMA (monosodium methanearsonate) is an arsenic-based grass killer. It kills grassy weeds such as crabgrass and goosegrass without harming most turfgrasses. It contains organic arsenic that, according to the University of Tennessee Extension, is less harmful than aspirin.
There are several styles of hearing aids available, from the smallest - Invisible in the Canal (IIC) to the largest and strongest - Power Behind the Ear (BTE), and the very popular Receiver in the Canal (RIC) - made to fit most hearing losses while remaining nearly unseen.
It is very common for people to get depressed and feel isolated if they are unable to hear properly and join in conversation. The vast majority of modern hearing aids, including those available from the NHS, are digital and designed to help people hear better in a variety of situations. You don't say how long your mum has had the hearing aid for.