That first image...she's not wearing power armor, so she's not a Sister. <3
I really, really, really do not want this particular thread to devolve into a discussion about Sisters and Slaanesh. (I say that and then I can't help myself.) Suffice it to say, the Sisters are a singular, mostly respectful representation of women in the 40k genre. Full (realistic) armor, motivated and dangerous warriors, they're really quite cool. One can make the case that they're still host to some (serious) representational issues, e.g. the Ms. vs. Mr. Pac*man* /Male is the Norm trope, but Sisters are still a step in the right direction. They are their own army and the only non-Astartes force that brings legit Power Armor and Bolt weapons to the party, both of which are canonical Imperium in my mind.
Slaanesh doesn't necessarily equate with sexualization, but when applied in fanfic and fan-art in practice - especially with regard to Sisters - I've found that it often does. Best case, it's easy and it's trite. Worst case, it's overtly oppressive. It really grinds my gears. :\
That said, her face was quite skillfully done, and the outfit wasn't that offensive; it's just obviously not a Sister, because power armor has an upper chestplate to go with those pauldrons. <3