You should go and google it - here is one hit: https://smartasset.com/financial-advisor/how-to-avoid-paying-taxes-on-an-inherited-annuity
Some portion of the annuity is generally taxable to you. The exact amount of the payment that is taxable will vary depending on many factors.
If you are receiving payments, you should also receive Form 1099-R from the company that is sending the payments to you.
As far as the RMD part of your question, you indicate that you are already taking the payments she was taking, it sounds like you most likely already have this covered, but it is difficult to say with certainty without other information.
If you did not get Form 1099-R please contact the annuity company for a copy. If you are just concerned about the RMD question in TurboTax, and you are taking the same payments that your mother was taking prior to her death, I would answer the question yes for now.
When you are able, contact the annuity company to confirm that the distribution you are receiving does in fact meet the required minimum distribution requirement.
Please accept my condolences on the loss of your mother.