moish, if yocheved thought amram was wrong for separating, because this meant neither boys nor girls would be born, then perhaps she would marry eltzafan to demonstrate that she disagreed with his reasoning. Just as he felt he had a responsibility, as the leader of the shevet, to demonstrate appropriate behavior for others, so perhaps did she. I am not saying this was necessarily the case (according to targum yehonason), just explaining how your argument can be turned around.
Also, regarding the issue of yocheved being forbidden to amram because she’d married in between, I seem to recall learning that this is not asur from the torah, but was made asur to discourage illicit behavior. If this is true, perhaps this would explain how amram would have been allowed to remarry yocheved even if she’d married someone else in between (especially since her motives would obviously have been l’shaim shamayim).