If you can live with the nowtv policy of a maximum of 4 devices and 2 streams at the same time, then yes you and your daughter can share the same nowtv account.
You need to decide which of the two accounts that you want to close, where you then need to cancel all passes individually that are active on the account you wish to stop using.
When you cancel the passes by going to My Account > Passes & Vouchers on here, make sure you follow all steps on screen until you get the green thumbs cancelled message.
If you then jump back to the Passes & Vouchers section it should show cancelled next to the pass with how many days left to watch the cancelled pass.
You should hopefully also receive an email confirmation from nowtv that a pass has been cancelled.
Would also recommend you add a payment pin by going to My Account > Settings and Pin's on both accounts where the 4 digit security code is withheld by the person who is responsible for paying the bills on the account.
Then with the stick that has the cancelled passes on it, navigate to the NowTV App on the stick, open the NowTV App and under the My Account section LHS of the TV screen above Help, click on it and hit the right arrow once on the remote where you will see a button to "sign out".
Sign out of the stick, then sign back in with the account details that you are going to keep between the both of you going forward.
Or another way is to factory reset the stick with the cancelled passes by holding the reset button on the stick for about 6 secs or go into the stick menu settings under the factory reset section.
Then when you setup the stick again from scratch use the nowtv account details that you want to use & keep.