This is my first vote of my own:
[x] This will change how she sees her own existence, and that of magical girls, for the worst; but yes, you think she can handle knowing the truth, whether she thinks she'll be able to keep the secret without letting it take control of her life and interfere with her, Madoka and Hitomi's friendship is up to her to decide; but she must know, you're working in fixing the issue, and while she could also help, and it would be appreciated, you're pretty sure you can do it on your own, so she must not worry about it if she decides not knowing.
-[X] The reason you wanted to tell her is because you don't want her to learn it throught Kyubey or other magical girls without you there to alleviate the blow; she could also help you prevent this ever happening to Mami, and you want to trust her not to be te one that does something that'll hurt her that much.
--[X] But you also fear her obssesing over it and allienating Madoka, Hitomi, Kyosuke and her parents without realizing it; no matter what, your first priority will be that your friends are happy and you don't want to throw a wrench at their friendship.
-[X] Homura also fears that she may do something that makes Madoka want to become a magical girl, she cares about her, and about all of you even if she doesn't know how to show it, for reasons you can't tell her.
Even if I know word count is only a guideline, the fact that I'm 95 words over it makes me feel that I'm not good a this, the two middle paragraphs are just there to explain the first.
[x] This will change how she sees her own existence, and that of magical girls, for the worst; but yes, you think she can handle knowing the truth, whether she thinks she'll be able to keep the secret without letting it take control of her life and interfere with her, Madoka and Hitomi's friendship is up to her to decide; but she must know, you're working in fixing the issue, and while she could also help, and it would be appreciated, you're pretty sure you can do it on your own, so she must not worry about it if she decides not knowing.
-[X] The reason you wanted to tell her is because you don't want her to learn it throught Kyubey or other magical girls without you there to alleviate the blow; she could also help you prevent this ever happening to Mami, and you want to trust her not to be te one that does something that'll hurt her that much.
--[X] But you also fear her obssesing over it and allienating Madoka, Hitomi, Kyosuke and her parents without realizing it; no matter what, your first priority will be that your friends are happy and you don't want to throw a wrench at their friendship.
-[X] Homura also fears that she may do something that makes Madoka want to become a magical girl, she cares about her, and about all of you even if she doesn't know how to show it, for reasons you can't tell her.
Even if I know word count is only a guideline, the fact that I'm 95 words over it makes me feel that I'm not good a this, the two middle paragraphs are just there to explain the first.