"Is the beneficiary spouse considered the owner of the decedent's IRA even though it may be several months more before the custodian gives her access to it?"
Upon the death of the participant, by operation of law the account becomes an inherited IRA maintained for the benefit of the beneficiary(s).
"Since the beneficiary cannot elect to treat an IRA as her own if she does not have access to it, does the IRS assume she didn't take the election?"
If the spouse beneficiary fails to complete a required beneficiary RMD as would be the case if no RMD is taken until 2026, the spouse is deemed to have treated the account as the spouse's own beginning with the year that the beneficiary RMD was not taken.
https://www.irs.gov/publications/p590b#en_US_2023_publink100089979
"The IRA custodian has told me that the RMDs are not required until the transfer process is completed"
The IRS custodian is wrong. Unless the spouse treats the IRA as the spouse's own or is deemed to have treated the IRA as the spouse's own by failing to complete a beneficiary RMD, this spouse is required to take beneficiary RMDs for the years beyond the year of death. Of course, since the intent is for the spouse to treat the IRA as the spouse's own, failing to take a beneficiary RMDs accomplishes the desired result. If a beneficiary RMD is missed, once the IRA custodian allows the transfer it must be transferred to an owned IRA, not an inherited IRA (since the IRA will already be deemed to be an owned IRA). (If the transfer occurs after the spouse's required beginning date for RMDs, April 1, 2027 if the spouse reached age 73 in 2026, late RMDs as owner will been to be taken and a request for waiver of the excess accumulation penalty made on Form 5329 Part IX.)
