Restrict texting on your daughter's phone if you are that concerned. Then set some ground rules before letting her use it again, eg., nothing gets deleted unless YOU delete them or something like that. Do a sanity check by verifying dates/times of SMS on phone with online account. A PITA for you, but if you're that worried, you should do it.
Alternatively, you could get her a phone that you can install My Mobile Watchdog
It's not spyware in that she will know that the app is on the phone. But you will get copies of everything she sends/receives. Solves the "illegality" issue that some folks are bringing up here.