When it comes to genetics, it's completely up to chance if the offspring share anything with the parents. There's a possibility they have the mother's eyes, the father's eyes, or a combination of the two that make them look nothing like either parent. You can say they are mother, and daughter, and that's all there is to it. They're your characters; You created them. You say it's so, then it is. I believe you. What would I do, argue with the author?
lol but if you want a better response, yea. They look close enough that someone can objectively just look at them, and maybe assume they're related- They might argue cousins, or sisters, but related nonetheless because Saver just looks young, or as young as Idk. That said, a Mother/ Daughter relationship isn't a far stretch at all, counting she had Idk at a young age. It happens.
You're fine; Like I said, you're the author, you say it, and it's fact. Done 'n' done.