My Mom is very deaf. If someone shouts at her, she can hear a little. What type of Dr. should I take her to?

I would first see an Eye, Ear and Nose Dr. You want to rule out if its built up wax or a physical problem. An audiologist is only needed when a hearing aid is involved. They fit and program the hearing aide. She will need to sit in a small room and the audiologist will ask her questions. She will then have to be able to sign when she hears or doesn't hear. My DHs insurance covers a new hearing aid every 3 yrs. We also need to use an audiologist they OK.

You can call an audiologist and ask if Mom needs a Dr exam first.

Your profile says your mom is 100 years old. Do you really think she will be able to:

1) physically manage hearing aids, which are very tiny?
2) learn how to use the hearing aids, which often are controlled by mobile phones?
3) afford hearing aids, which are not covered by insurance and can cost upwards of $3000?

Also, if she has any cognitive problems she may not even be able to answer any of the doctor's questions accurately.

On this forum I have read about hearing amplifiers that are more affordable and easier to learn how to use.

I did a quick search and found this article that names some devices:
https://dailycaring.com/affordable-hearing-aid-alternatives-for-seniors-hearing-amplifiers/

Others on this site have experience and will provide more specific info for you.

I have never been to a bad audiologist. Locate someone and make the appointment. Maybe she can be helped. You could also go to an ENT doctor. Mine has an audiologist on staff for testing.