Complex sentence: While taking the promicin inhibitor her ability only worked on children, but without the inhibitor she can help adult 4400's focus their abilities, e.g., she helped Richard Tyler gain greater control over his telekinetic abilities.
Split into simpler sentences: While taking the promicin inhibitor her ability only worked on children. Without the inhibitor there is evidence that it works on adults and that she can help other 4400's focus their abilities: she helped Richard Tyler gain greater control over his telekinetic abilities.