I am very sorry to hear about your mom's passing. I hope that your family and you are doing ok during this sad time.
Regarding your question, here is a note from the IRS:
From the IRS: An individual who died in 2021 or in 2022 and did not receive the full amount of the third Economic Impact Payment may be eligible for the 2021 Recovery Rebate Credit if the individual met the eligibility requirements while alive.
Since your mom passed away in 2021 you should be eligible for the third Stimulus payment.
Hope this helps answer your question.