Hi there
I’d be happy to help with your call/message records activity question! The only way to make a call or send a text message without a record of this showing on your online account would be to not use AT&T call/sms service for the action. To explain, depending on the device she is using, she may be able to use apps which provide call or messaging features over a WiFi or Data connection. As the information is passed through data, the specific action would not show on your account, just that data had been used.
If she makes a standard phone call or sends a normal text message, there would not be a way to prevent the record from appearing on myAT&T or your bill.
I hope this helps!
Charise