I don't think she needs a girlfriend - she's a strong, independent, character. And the second movie is a bit late to suddenly add it in. So, I'm not really on board with this.
However, I do feel that there needs to be at least a couple of main characters that aren't 'Mainstream white, straight and cisgendered' in the movies out there - and yes, the Disney ones too. Why? Because kids are growing up aware they are different to some of their friends and that they aren't represented AT ALL in the movies they and their friends watch.
It was like this growing up for people like myself - Disney was all white princesses finding a prince....what if you're a non white person? Are you not a princess? What about if you didn't want a prince but a princess? (Or a prince instead of a princess). Many gay adults have commented that they felt left out, ostracised by films when they were young....when they knew they were different, but couldn't quite put a finger on why...but no one was representing them in the popular media, so it was as though they were alone in the world in feeling this way.
Now, I know you, Loli, personally feel it's a choice to be gay. And I as a gay person can catagorically say it's not - if we put that all aside - these are kids who are feeling alone, ostracised by Disney, Pixar and their friends because they know they are different - even if they don't have the words for what it is that makes them that way - these are kids we lose to suicide, and self harm because they feel that no one understands what's it's like to be them....
We need to represent them in these movies. Not all of them, I'd never ask for that. It would just be kind to have a couple of main characters every few years be slightly different to the straight, white princesses we have forced on us. There are a few in the current movies at the minute as small characters - Wandering Oaken in Frozen has a family and a male partner (check the sauna shot), and Findingn Dory apparently had a lesbian couple with a baby as a small part - so we're getting there.
(Before you try the 'but it'll make them gay..' - it doesn't work like that, and we adult gay people are surrounded by straight people growing up - didn't make us straight)
Also - I've avoided answering yr questions in the past, because of the way the comments end up. I'm answering this with respect and honesty, and putting aside any disagreement we may have had. I hope others can do the same.