Yes, you must do so. You need to pay levy up till the date she is transferred to her new employer. Thus, levy will be charged even if you sent the helper back to the employment agency while she waits for the transfer.
The process of finding a new employer may take a few weeks, so you should check regularly with the employment agency on the progress of the transfer.
Once her new employer issues the Work Permit, we will automatically cancel her current Work Permit and stop your levy biling.