Lina can get pregnant at the end of her corruption level 4. The move to corruption 5 (which has no content) is a little buggy for now (low priority cos no content), but it's to do with her sex tape.
There is a sperate check at the end of the run that detects if you've gotten alex pregnant at C5 (sex 3 times and talk to her in the forest) and lina pregnant during her sex tape scene. Then there are many derivations of that depending on how breast expanded they are.