Did she consult Oticon support to get suggestions from them to try out?
If your sister is of normal hearing and couldn’t help your mom’s phone ringing, then I’m not sure your hearing aids would help make you hear better than your sister’s normal hearing anyway. Perhaps your mom’s ring volume is set to a very soft level to begin with. But you need to have the expectation that while the hearing aids may help you hear better, it’s not going to help you hear better than what a normal hearing person can hear. At best you should just have the expectation (and hope) that you can hear better than without them, but never as good as normal anymore. So I think that you may be right that you might have set your expectation for your hearing aids too high.
You do have moderate hearing loss at mid to high frequencies, though. So at the very least, when listening to music via a good set of speakers, you should be able to do A/B comparison by turn on/off the hearing aids (or take them out and put them back in) and be able to discern “some” difference. At least you should hear higher frequency sounds from the music a little more clear. If not then something is wrong and you should go back to your HCP and do some more of this kind of testing in front of them so they can make more adjustment for you.
As for normal everyday situation, maybe the difference is more discernable when you’re in a noisy place and try to listen to people talking. If you’re at home where it’s more quiet and not noisy, you probably can’t tell much of a difference. So try to find noisy places to go to and do A/B comparison test (by simply turn on/off the hearing aids) and listen on the fly to see if you can hear a difference.