Assumption of ownership of the remainder of the inherited IRA should have been accomplished by a nonreportable trustee-to-trustee transfer and the gross amount on the Form 1099-R should have been only for the RMD. However, it seems that the broker instead moved the funds into your name by making a distribution of the entire inherited IRA and rolling over to your own IRA the amount in excess of the RMD (not by assumption of ownership). This subjects the distribution to the one-rollover-per-12-months limitation whereas a trustee-to-trustee transfer would not.
As a distribution and rollover, enter the Form 1099-R as received. Indicate that it's an inherited IRA that you inherited as spouse of the decedent. Indicate that part of the distribution was RMD and enter the amount that was RMD. Finally, indicate that you moved the money to another retirement account, that you did a combination of rolling over, converting and cashing out, then enter the amount rolled over to your own IRA. TurboTax will include the entire amount on Form 1040 line 4a but will include only the RMD amount on line 4b and will include the word ROLLOVER next to the line.
