My 94 year old mother wants to do her own taxes and bill paying, despite poor eyesight.

Your mom is not incompetent if the only reason she can’t pay bills is failing vision. She is just old. She got to be 94 by making good decisions for herself. She probably feels good about her ability to still be independent in various ways. I’m sure it causes you anxiety that she won’t turn it over but really what is the real harm? IRS allows amended returns. Companies send late notices. It isn’t the end of the world. If something happens you could volunteer again. If she does have dementia (and not all elders do) it will progress and be more evident as time goes by. Do you bring her mail to her? easy enough to monitor right?
Perhaps you could help her do them her way instead of changing things she is comfortable with. Just a thought.

I like the idea of having something she can see. My Moms bank statement showed money coming in and going out. Get the ones that are from when you started. Show her the balance at the time u took over. Then show her each payment you made and to whom that was made to. Coming to a balance carried over to the next month. Then she will see you are not stealing. Taxes, you have till next April to worry about that. Maybe instead of doing them on-line you sit with her and do them. Maybe you should go back to writing checks and sit with her while you do it. Can she still sign her name?

Taxes are a bear! OH MY GOODNESS! I would never do my own taxes (unless its the easy one) but seniors have deductions and also because she is blind she gets extra deductions.
If she needs something to be in charge of let her organize the paperwork for the taxes but tell her that the tax guy needs to get her the most money back and the best deductions.
She can also be in charge of setting up her kitchen putting the cans in order or get her into a hobby - painting something easy organizing paint supplies. Gardening organizing the supplies. Try and get her mind off the money part. My example - my daddy was so worried about his money he wanted it at the facility he was in and I told him he could not have it but it was safe under the house and no one (I would whisper) knew where it was. I took a picture of a box under the house and told him the money was safe. Blessings

You have choices here. Either offer to take her to an account who will do her taxes and pay her bills for a fee, or let her make a huge mess of her bills and taxes because she wants to be stubborn or thinks you're incompetent and stealing from her.

Then leave her in the mess she makes. Let her explain to the IRS when she gets audited. Let the electric company turn her lights and gas off for lack of payment. APS will come and she will have to accept help then. Or accept placement in a supervised living facility.

I am sorry to say that many adult children are living in constant crisis mode waiting for the other shoe to drop with our parents. For the next catastrophe to happen. Many times the only thing for it is to let it happen.
Usually things have to get a whole lot worse with an elder before they can get better and any actual plans can be made to suit their growing needs.
Take a step back and let her do it her way for a while.

That is dementia talking to you, she has lost her ability to reason.

I would supply her with printed information as to what you are doing, that seems to calm them down, don't forget they did not grow up in the digital age.

My mother is 98 and she still wants to see her checking account statement, so it is sent to her, my brother and I view it online if need be.

Exactly as Funky said:
Don’t make it obvious you’re doing it.

You can lie: example:
”I didn’t do your taxes. It turns out that from age 94, the government automatically does it for you.”

Your mom isn’t thinking straight: she’s forgetful. You must decide what’s best to do. You take over.

YOU know whether you’re doing it “dishonestly or incompetently”. If you know you’re doing it right, just continue.

Can you not have her sit next to you while you show her on your/her computer exactly what is coming in and going out so she will have more peace of mind?
Just a thought.

The suspicion that folks are stealing is a common feature of some dementias, especially at the early stages.

Has mom been seen by a geriatric psychiatrist or neurologist, or neuropsych for evaluation?

For some folks, repeated reassurances can be enough. For others, medication can help.

Perhaps your mom wants to feel included in what’s going on.

My mom’s vision wasn’t as good as it used to be, plus her tremors from her Parkinson’s disease didn’t allow her to write very well. She missed being able to send emails back and forth to her brother in another state. As her Parkinson’s disease progressed she couldn’t use her laptop.

My mother mourned for her loss of ability to function as she did before. Still, she liked being updated on situations and was grateful that I was able to help her.

When I took over my dad’s finances, I expected total anger from him. He’d always been very independent in handling money. When I showed him a literal 3-ring binder I’d prepared with a bill paying sheet for each month, with name of creditor, amount due, date I’d paid it and how it was paid (check, online, cash) He happily looked through it all and could see easily that nothing was amiss. I updated it often and he looked it over often, but he never was doubtful or angry. Hopefully you’re showing mom in concrete form all the information on her finances