If you are less than 10 years younger than her, you're an Eligible Designated Beneficiary. Since she was under 72 at time of death, you can choose 1) Lump Sum cash out, 2) Life Expectancy Method (and RMD must start by Dec 31 of year after death), or 3) 10 year method (full distribution by Dec 31 of 10th year after death). If you had not been an Eligible Designated Beneficiary, you'd have to use the 10 year method.
Sounds like, if you did not take RMD by Dec 31, 2021, then you chose the 10 year method. If you didn't mean to choose this, you need to take 2021 RMD immediately (and don't forget to take 2022 RMD in a separate transaction). File form 5329 with your tax return which will report a 50% additional tax on the late 2021 RMD, but don't pay it- attach a letter explaining why you didn't take RMD timely (i.e., you didn't know you had to, you have since taken it, and you will not mess up again in the future). Hopefully they waive it and you won't owe the tax. If not, you'll get a bill for the tax plus interest.
I think you have to calcluate RMD yourself since this is not an employer sponsored plan. Try
here to help.
Source: I'm a tax attorney. But not YOUR tax attorney. So, take my knowledge above as a starting off point to do some research on your own.