1) There was no one else available. And even with Sharingan, Sasuke was not a "major priority" for Konoha.Originally Posted by CapsuleCorpJX
2) She knew that the only way to stop them would have been to beat them up, arrest them, or brand them as traitors (for going against her orders). Either way, they would end going. So she allowed them to go when Kakashi offered to check on them.
Besides... this is shounen manga... learn to know "main characters" never follow their orders.