What on earth the ATCO was doing clearing the USAir for take-off when she didn't have a positive fix on the United is beyond me!!
In my read of what I heard, she felt that she did have knowledge of where United was, and after several exchanges was convinced that she was correct.
and as it turned out was she not right in that point
So if my read is correct this a a procedural (what level of information is necessary to make a decision) issue rather than a castigation of the controller