True, but at the same time FMC was the one "in charge"...and the maid betrayed her; plus, to save FMC the maid put Elsa's life in danger...and Elsa's life is invaluable, for FMC.
So basically she betrayed and endangered someone dear in the process.
That's too far even with good will behind to let it pass so easily
That's how people work, I suppose. We are selfish in nature, we only think for ourself most of the time and I see no problem with miss elf choosing to prioritize the people she cherishes the most at the risk of Yvonne's feelings.
Of course, one can choose to forgive or not to forgive. But because Yvonne understand miss elf's point, she chose to forgive and I think this is inline with her charater settings, adorably sweet. Remember that many times over that Yvonne would rather choose to harm herself than to choose options that hurt Elsa via the system mission prompt. That was even before she had any feeling for Elsa. She is just that good. This time, Yvonne mother is at stake, that's the dilemma here, mother or lover. This allowed Yvonne to be "easily" forgiving, had it been anyone else, I wouldn't think so and would gladly agree with you. Elsa also knew that Yvonne herself would have bear her mother's curse if she didn't do anything and with a normal body like Yvonne, she would have met the same end as her mother. The author is hinting that Elsa can somehow solve this problem with her thick plot armor because I don't think the author want to kill off neither Elsa nor Yvonne. Most of the time, our perspective is from Yvonne's pov, thus, it's easy for us to forget that the one having the biggest plot armor to this point is Elsa so I would like to believe in our little Elsa.
And finally, I think this is a necessary step to achieve consistent timeline. This would explain why Elsa is so obssesed with Yvonne at the beginning even through all of those "bullies". There is a reason for Elsa's action and this could be it.
