In the Supergirl tv show, Kara arrives to Earth around age 12. So, she should start gaining powers from the moment she arrives. While Clark will have at least 10 years to live a semi-normal life before the development of powers. Also, by this time Kara will be old enough to have moved away from the farm or gone to college. Would she postpone *her* life as Clark will be just be gaining his powers, so she can help him through the transition? Would any of this cause strife between them?
"On the long road, take small steps." -- Jor-el, "The Foundling"
"clearly there is a lack of understanding between those two... he speaks Lunkheadanian and she Stubbornanian" -- chelo.