Do you think Ahsoka could’ve stopped Anakin from turning to Dark Side? Or turned him back if she’d gone to Mustafar instead of Obi-Wan? They both saved younglings on Mustafar once.
No, I don’t think so. I think the only person that could have stopped Anakin from turning to the dark side is Anakin himself–setting aside Palpatine being the one to make the offer and, if the offer weren’t there, Anakin probably wouldn’t have turned, but that doesn’t make it any less Anakin’s choice.
The reason Anakin turned is that his fears consumed him and his belief that Padme would die in childbirth and that he couldn’t let go of those fears, the fear of the loss of her, and Ahsoka couldn’t have mitigated that by being there. Hell, Padme couldn’t mitigate that by being there! She told him that they were just dreams, she poured all of her love into him, she begged him to run away with her while they still could, even after he’d murdered the Jedi and the younglings. If that couldn’t turn him back–when she was the focal point of his fears and reason for turning–nothing anyone said or did could change Anakin’s mind.
The problem wasn’t that there was something logical that could be done that wasn’t being done–like, Padme going to see an OB-GYN (which she did in Legends and I think makes sense that she would) wasn’t going to matter to Anakin, she could have had a dozen doctors all saying, “She’s fine, the baby will be fine.” and it wouldn’t matter. She could point out (and did in Legends, iirc) that women just don’t die in childbirth on Coruscant, and it wouldn’t matter.
Because it wasn’t a rational fear, it was based solely on dreams he was having. It was because Anakin was consumed by that fear–”Just help me save Padme’s life. I can’t live without her.”–that he fell.
And once he fell no one could save him, because he knew what he’d done was wrong and he knew he was justifying it by saying it was for Padme’s sake, when really it was for his own.
Anakin is lying to himself about the truth of what he’s done, he can’t admit that it was the wrong choice, because then he’d horribly betrayed everyone and forced them to act against him, and he couldn’t tolerate that.
He couldn’t tolerate that people would look at him and see the faith he’d broken in him, he hated himself so much that he was crying on Mustafar and no amount of Padme pleading, “Come back, I love you!” could save him, no amount of Obi-Wan desperately trying to hold off in the fight or trying to break through to tell him, “Anakin, Chancellor Palpatine is evil!“ or pleading with him not to make that fateful jump was going to save him. Ahsoka couldn’t reach him any more than Obi-Wan or Padme could.
Ahsoka is deeply important to Anakin, but this wasn’t really about someone failing to save Anakin, it was about Anakin refusing to make better choices because he let his attachment–as the Jedi define it, that inability to let things go when the time comes, to not burn down the galaxy trying to stop death, that is what they mean by attachment–consume him and the fear that he would lose Padme, regardless of what she would want done on her behalf or not done on her behalf, drove him to be unable to admit he made a horrible, horrible mistake. Ahsoka couldn’t have changed that, certainly not if Obi-Wan and Padme combined couldn’t even dent Anakin’s determination to stay on this path.