QUOTE(rqwrqw @ Jul 22 2017, 04:50)

It sort of literally says that (albeit still shitty grammar for a literal translation), but a closer English approximation is something like "I'll pat you on the head for being good girl" (where "I" refers to the "big sister", so depending on the actual relationship here, "Your big sister will..." instead of "I'll" would also work).
いいこいいこして refers to the act of affectionately patting someone on the head and telling them they're a good boy/girl, but literally says "doing 'good girl, good girl'" (at least when being done to a girl).
Note: She's speaking with a non-standard dialect as well, if that matters.
Thanks.