I dislike Leia being Luke’s sister too as it feels as a forced retcon, but they had no choice but do something about it. Had Yoda just said “We need to find another one”, no problem, but he didn’t, so they HAD to explain who was the “other” he was talking about.
Anakin? Not sure it would’ve worked, as Yoda refers to him as an “agent of evil” in TESB, but with the right dialogues, they could’ve made it believable maybe (hell, they “kind of” explained why Ben lied, after all!)
If they didn’t have so many characters at that point, they could’ve introduced her in ROTJ as a new character working for the rebellion, so to make her take part to the DSII attack. I’m not sure it would’ve been better, but from a marketing standpoint, this could’ve also been the basis for new films or telefilms.