German Translation
Das habe ich ihr schon oft gesagt.
Why is “se” necessary here?
Update: I initially thought that se was a reflexive pronoun (itself/himself/etc.), which is why I got confused as that seems misplaced here. It turns out that se in this context instead takes on the meaning of le (“to her” or “to him”).
I think, if you were to ignore Spanish grammar, this sentence would be:
“Eso ya le lo he dicho muchas veces.”
“le” (“to her/him”) in place of “se”, which I can understand.
But apparently there’s a rule that if “le” or “les” occurs together with one of “lo/los” or “la/las”, then you say “se” instead of “le/les” because otherwise it would be difficult to pronounce combinations like “le lo”. (Also described here under Etymology 2.)
Hope this helps any other beginner. 