I'm not a lawyer and I didn't read VA rules but it sure seems to me you are doing it the hard way!
Its well established that if person gives something away while alive its simply not there for distribution via the estate. Common example, Car is willed to son but before person passes they sell the car--the car is simply not there to deliver to son and it never comes into executors control either. No car to deliver!
For all you know, Mom could have gifted the table to Sis or the mailman several weeks prior to passing---it simply never became part of the estate you took over to manage..
Now if it and other gifts to Sis exceed $13,000 in that year you may need to account for tax issues but thats another story.
If Mom gifted it early that also should be end of story. True if it was taken after Mom died and you were in charge its your duty to recover it,if its to be recovered, but al least for now that doesn't seem to be the fact pattern and even if it was you have no proof of it was stolen--for that matter you probably don't have any proof it was in home at time mom dies--your post suggest it was gone earlier.
Again, for all you know, Mom make a gift a few weeks before she passed, if Sis asked Mom may I have my table now and Mom said yes,--why take it to some illogical extreme.
So far your quest for technical perfection has cost estate $750 down the drain--not very wise?