"qui t'a donné la vie"

Question

My questions are about the sentence, "Et puis, une mère n'est pas uniquement celle qui t'a donné la vie.": Why is 'te' used here instead of 's'a', 'l'a' or some other construction, since it seems to be some kind of generalisation? And also, if 't'a' is used and the speaker is talking to another woman, why doesn't 'donné' agree in 'donnée'?

Maarten Kamp · Accepted Answer

Sydney, 
The expression is ‘ donner la vie à qqn ‘ - therefore, the pronoun to replace ‘ à qqn ‘ must be an indirect object pronoun, excluding “ l’a “ from the possibilities. 
With respect to using ‘ t’a donné ‘, I think this is colloquial, and natural in the context.
This is a discussion between friends, and the speaker has chosen to use the informal, singular form of ‘ you ‘ addressing the listener, and also not to use the formality of a depersonalised general statement.
Similar to saying in English  ‘ a mother doesn’t have to be the one who gave birth to you/brought you into the world ‘. 
The direct object in the expression ‘ donner la vie à qqn ‘ is ‘ la vie ‘ and follows the verb, so there is no past participle agreement in compound tenses ( passé composé in this sentence ).
 https://progress.lawlessfrench.com/revision/grammar/special-cases-when-the-past-participle-agrees-in-number-and-gender-when-used-with-avoir-in-le-passe-compose-conversational-past