Why "se" lo manda a ....

Why "se" lo manda a ....
 

can someone explain the rationale behind the "se" in the following:

ya se lo mandó a ella?
se lo voy a enviar a la mia

"Se" is an indirect object pronoun referring to "a ella" and "a la mía". They're redundant, but sometimes the speaker finds them necessary.

"se" replaces the usual "le" when in front of a "lo" o "la" direct object pronoun so that's its easier to say

Exactly. It sounds better. That's the rationale behind the use of 'se' in this particular structure.