Padme fakes her death, takes Luke to Tatooine with Ben to arrange things with Owen and Beru, goes with Bail to Alderaan to raise Leia, assumes new identity, dies of natural causes, (or an accident) while Leia is still a toddler. Problem solved.
That would take too much screen time after the climax. That would take a whole other movie. Also, why would she leave Luke with Owen and Beru if she was still alive. Why wouldn’t she want to raise both of her children herself?
How so? Put her into the discussion scene on the blockade runner, where Yoda convinces her separating the twins is a good idea, and to let the galaxy think she has died. Padme tearfully agrees, as the situation is too dangerous to keep them together right now. She realizes Tatooine would be a good place to hide Luke, at least until he’s older and can start training. (She’s already met the Lars.) She requests Obi Wan to watch over Luke.’
Padme’s death doesn’t have to be explained on screen, as Leia already stated she died when Leia was very young.