I'm sorry to hear of your mother's passing. Condolences to you.
There are two possible tax returns that need to be filed.
One is the final 1040 of your mother.
The second is a possible Form 1041. The year begins on the first day after your mother's death in July of 2017.
You can choose to make it a short year and end it December 31, 2017; which would make it due April 17, 2018.
Or, you can choose to have the year end June 30, 2018. (or another month end date before June 30, 2018; but not after; you can't have a return period longer than one year) Which would then be a due date of October 15, 2018/
Here is a link to Publication 559. Look under when and where to file.
https://www.irs.gov/pub/irs-pdf/p559.pdf
If you choose a fiscal year ending in 2018, you will need to manually maintain records of income expenses, etc. for the months in 2018.
Also, statements for your mother's 2017 1040 may or may not be correct. Some statements may contain income received by the estate. Thus, they'll need to be reported on the 1040 as gross, and then reduced for amounts reported on the 1041. IMHO, this is best done by attaching a statement.
**Disclaimer: Effort has been made to offer correct information; but due to the discussion forum limitations, the poster disclaims any legal responsibility for the accuracy of the poster's response**
