Death Claim and Spousal Assumption/Rollover

Does anyone know or be able to provide a source. I have a sole spouse beneficiary of a qualified plan worth around $500,000. She wants to take $200,000 and move it to a Roth IRA (so do a spousal assumption of $200,000 into a IRA and then do a conversion once the funds are in a Traditional IRA in her name) and move the $300,000 and keep it as a beneficiary designation so she wants it moved to a Inherited Traditional IRA FBO her benefit. Can a sole spouse do a partial spousal assumption of the account?