When they found that the attacker, Ark 15 has gone to Proxima B itself, they decided not to go there and to go to next nearest exoplanet Ross128b. It lead to dispute with Dr. Trust. But, Centauri system has 3 stars and 2 confirmed and a third unconfirmed planet and there may be more planets that could have been discovered in the futuristic of the series. So, instead of adding many light years of travel by going to Ross128b, they could have gone to these other planets of Centauri system itself and could have kept vigil on Ark 15 from there and made plans to defeat them eventually, while Ark 15 people wouldn't be any wiser that Ark 1 has landed on a nearby planet. By the logic and knowledge of Ark 15 people, they have already destroyed Ark 1.
If you compare the build of Kelly and the engineer she murders, it is highly unlikely that she would have been able to lift him into the ejection chamber. Also, it seems strange that none of the engineer's colleagues are missing him.