Leia was a beloved character from the start
As far as most fans are concerned, Leia Organa is an absolutely beloved character and always has been. She's a take-charge, badass woman who rescues others as much as she gets rescued, and doesn't take crap from anybody. There's a reason that Leia's a feminist icon — even when she's put in a weird gold bikini to be an alien slug's slave, she ends up choking the actual life out of him.
Thing is, according to no less than Carrie Fisher herself, Leia being a beloved icon from Scene 1 on was not the case. In a 1983 interview with Rolling Stone magazine (the one with possibly the greatest cover of any publication in the galaxy), Fisher revealed that the writers struggled to make Leia easy to relate to. Because she had lost her planet and everyone on it, Fisher said "all she has is a cause" and that for the writers, the "only way they knew to make the character strong was to make her angry."
Therefore, the same strength that many fans love about Leia left a lot of early fans cold, and Fisher said they thought she was "some kind of space b****." According to her, Return of the Jedi involved very deliberate reinvention of her character, where she "gets to be more feminine, more supportive, more affectionate." (This would explain her more pronounced romance with Han, friendship with Ewoks, empathy with Luke, and so on.)
The ironic downside to softening her character, however, is that because these movies were presented as "basically boys' fantasies," the filmmakers felt they couldn't fully feminize Leia without having "her take off her clothes" — hence, the infamous gold bikini was born.