It's very possible Mom installed some software on the phone that allows her to track the phone, and you can't find it in the phone to turn it off.
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This service will
1. Track all to/from calls
2. record those calls
3. Track all texts in/out
4. GPS
5. record all audio even not during calls. Just all the time.
The only way you can get around it is to turn off the phone. Or leave it in a drawer, as mentioned.