You don't choose a target for Taeko's last ability at the time it triggers. Rather, a second "reflexive" ability triggers when you pay {U}{B} this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.

If Taeko leaves the battlefield or dies at the same time as one or more other creatures you control leave the battlefield without dying, its second ability triggers once for each of those other creatures. You will scry for each of those other creatures, but Taeko will not be on the battlefield to receive +1/+1 counters.