Rashi on Genesis 29:12/רש"י על בראשית כ״ט:י״ב

1כי אחי אביה הוא HE WAS HER FATHER’S BROTHER — near kin to her father, as (Genesis 13:8) “for we are men, brothers (אחים)” (i. e. near kin). A Midrashic explanation is that he meant: if he (Laban) intends to practice deceit upon me then I am his brother (a match for him) in deception; if, however, he is an honest man then I, too, am the son of his sister, the pious Rebekah (Genesis Rabbah 70:13).

2ותגד לאביה AND SHE TOLD HER FATHER, because her mother was dead and she had no one to tell except him (Bereishit Rabbah 70:13).