Of course, one could just say that SH was sloppy and didn't care about the access key, if Rand is captured.

SH says to Semirhage: "You were to capture the boy, not kill him." (Moridin states the same in the prologue) Then SH says that Semirhage has one last chance. Combining it, it's meant it is her last chance to capture Rand, and this is also how Semirhage understands SH's order; torturing Rand is just something Semirhage does, because she has the opportunity.

The problems I have with the DO's plan to force Rand to use the TP in the way you suggested are:
that Moridin likely wouldn't tell the DO anything about the bond before, because he might gain the mistrust of the DO; that Moridin couldn't know if Rand would be able to channel the TP via the bond; that Moridin couldn't know if Semirhage would really bring Rand in a situation, where he has to channel the TP, because her order simply was to capture Rand; and that the DO is a control freak, who doesn't know what will happen if the Creator's Champion channels the TP.