Just as a tip, shouting or even just speaking more loudly is rarely necessary if someone has (properly configured) hearing aids. Just speak clearly. Ensuring proper enunciation so they can read lips is usually more important. Hearing aids will make it "loud enough" but they won't clean up the information.

Does she have primarily high frequency loss? High frequency loss is the most typical in the elderly and also from damage from noise exposure.

Different people have different voices. I usually find it easier to understand men because I hear the lower frequencies better, especially without my hearing aids but also with them. And it's always easier to understand people you know well compared to strangers.

I find small speakers to be awful. The high frequencies are distorted and tinny. Scratchy is a good way to put it. I have a very hard time understanding anything played through a smartphone or tablet speaker. The speaker is too small to reproduce the bass frequencies I can hear the best, and so it's just TSSST TSSSSSZZT sounds through my hearing aids.

I cannot wear my hearing aids at full volume at the dinner table or while working in the kitchen for this reason. Metal, plastic and paper are also common offenders. CLINK. CLINK. CRSZZST. It's almost painful and headache inducing if I'm tired.

Unfortunately those high frequencies are what carry speech sounds like sh, t, ch and so on. Without those it's like the adults talking in the Charlie Brown cartoons. "wah-womp-wah-wah-mhuh??"

Hearing aids can do two things for this: one is to take some of that high frequency information and remap it to lower frequencies. This is part of why they say you won't like wearing your hearing aids when you first get them. They're systematically distorting what you hear -- but in a way you might eventually learn to interpret.

The other is just to make it loud enough that it can be heard. And as you suggest that may be the limit of the hearing capacity if there's very little at the high frequencies the only way to make something high frequency to be perceived, is to hammer the ear with a 90 or 100 dB level of sound.

It's absolutely worth having them adjusted a bit. Also every manufacturer uses a different algorithm for speech frequency remapping. Some people have strong preferences by brand as to the hearing aid sound. (Phonak and Oticon certainly have different "feels" in my experience.)

Almost all hearing aids allow multiple "configuration profiles" where you can switch through them with the app or buttons. I have four: general, lecture, comfort, music. Comfort mode just nukes the high end and cranks up the noise reduction. That's what I use if I'm just reading alone in the living room, or when out at the grocery store, etc.

As to large groups, personally I've simply conceded I can't do large groups. If I try I will feel left out and get depressed over it. If people want to see me at a family reunion, for example, after I do a brief tour to say hi to everyone, they'll have to join me for a small group chat in the den or whatnot.