No, I was just taking Maou's statement (the one that said "Isis promised to give Seth to Osiris if the undead Osiris impregnated her with horus") to mean that Maou was talking about the rumor that Isis had the undead Osiris' child -despite knowing everything that Osiris had done- because the two had made some kind of secret deal (that time when she supposedly recovered his body parts from the Nile and and revived him for a while).
And also the whole thing about isis wanting horus to be safe that is true but her initial reason for birth of horus is for revenge why do you think isis will want the child of that fucker after everything she experienced. Of course our opinion may vary so let us see how the story go as it all depends on s2 and what we are doing now is brainstorming s2 so meh
Because she loved him and had just figured out her husband was evil, also feelings aren't so simple, you can't just stop loving someone by turning off a switch. After the time slip we see a more mature Isis, who sees Horus as his own person, not as Osiris son, she wants revenge from the things Seth did to her and Horus (although it's implied she also wants revenge from the other gods who ignored her)
I have a suspicion Isis wanted Osiris' child not so much for revenge against Seth (even if she spitefully wants Seth to think it that way) but because she wanted a child that would inherit some of Osiris' tremendous power, but none of Osiris' mindset (because she would be raising him all by herself, teaching him only her own principles). A child he could raise to be both powerful and just... In other words, the ideal type of king that Egypt needs.
Neither Osiris nor Seth were that for Egypt, as they both used Egypt for selfish reasons: Osiris covered Egypt with sand, eliminating lots of fertile land, just so he could bring Seth closer to him; while Seth used humans as tools and punching bags whenever it suited his fancy. Isis, however, wanted to raise an ideal king candidate (Horus) that could give Egypt the chance to be saved.
As for her using a flood to drown everyone in the corrupted realm, if she can not save it, I think that's supposed to be like the Great Flood in the Bible, where it was done in order to give the land the chance to recover and begin anew. The fact that Sekhmet mentioned Isis and the rest of the gods also used the floods in the past, to turn over the human popullation, probably means they used them to keep the popullation overgrowth in check in order to prevent scarcity of food, and the wars that would come with it, among the human popullation in a pre-modern society such as Egypt, devoid of modern technological advancements (look up "Malthusian catastrophe" if you're skeptical). So, they weren't supposed to be using their godly "license to kill" just to suit some selfish reason, like Osiris and Seth both did.
At least, that's my interpretation of the whole thing.
It was said that is her last resort. Besides, she made it so that Horus would be able to survive that so he could rebuild a new Egypt some day, even if the current one was destroyed. Isis' flood sounds a lot like the Great Flood in the Bible, which was supposed to cleanse the Earth and let mankind begin anew, and not completely destroy them.

I feel so bad for Isis, she is the ultimate victim, it's so refreshing to see a good female character in a MLM comic, although her life is tragic she has managed to survive and continue to protect her family
I mean I also feel bad for Seth but he has also done shitty things