Agree with Peter. But I know from experience that TIAA will not "treat that estate’s ultimate taker as if she were the plan’s beneficiary or at least a distributee".
Also, this sounds like a non-ERISA 403(b), since the spouse is not the default beneficiary. If they are saying the estate is 50% beneficiary, they should be able to explain how and why they cam to that conclusion. Assuming they are right- she might be able to rollover any distribution (made to the estate), to her own IRA ( many PLRs have allowed such rollovers). In this case, it would be her treating herself as the distributee- but she must consult with her CPA or attorney with expertise in such rollovers before completing any such rollover.
No- there is no such thing as a see-through estate. PS; the See-through trust would affect only the calculation and the option for rollover. Generally, rollovers are not permitted for estates, but the IRS have made exceptions in cases like the one you describe.