This sentence expresses a habit or a general truth, so we use the Simple Present Tense.
Structure:
Since My mother is a third-person singular subject (she), the verb tell takes -s:
I tell
You tell
We tell
They tell
He/She tells ✅
Why the other options are wrong?
❌ tell – used with I, you, we, they
❌ telles – incorrect spelling
❌ tellings – not a valid verb form here