Okay, I'll start this off with sharing my views on Gilda. I do somewhat find her interesting, what with her relationship with Rainbow Dash, fiery personality and the fact that she's a freaking Griffon! However, I do have an issue with the popular fanon on her that often tries to, like Trixie, portray her as some tragic figure with a bad past or even worse, just "misunderstood". Now yes, I agree she could have a temper problem and the way Pinkie Pie kept intruding was easily annoying in anyone's POV, but she was still openly antagonistic towards her when she could have politely asked her to leave them be, and was also openly antagonistic towards all of Rainbow Dash's other friends and associates, all by choice and seemed to take a certain sense of satisfaction in it. And in the end, she had a clear choice; be a bigger griffin and apologize and thus keep her relationship with RD in tact, or just walk out like an immature chicklet and thus potentially permanently wreck her relationship with RD. She chose the latter of her own accord. So in the end, she's not misunderstood, she's just an immature punk, only slightly better than the teenage dragons. At least, that's my view on her, and with that in mind, I think she has a bit potential, enough for her to appear in another episode.
So the question is what could the writers do with her that would be worth having her return? The way I see it, it would definitely have to a RD episode, or at least Pinkie Pie episode, because those are the two ponies, in the Mane Six especially, she has the most significant relations with.
As for the conflict that brings Gilda to the ponies again, that is entirely up to the writers. One speculationI believe I heard in the past is that Gilda is accused of stealing something from the Griffon King (or Kaiser as I like to think of their leader as) and RD has to decide whether she should help her ex-friend or not. This is a scenario I wholeheartedly endorse as it could be executed very well and potentially give us some more world building. Who here would just love to see the Griffon Kingdom? (I kind of envision it as something like old Germany or France).
Her relationship with RD would most certainly have to further examined in her return, as well as whether it can be salvaged, or whether the two even want to salvage it, considering their falling out and how much things have changed. The ending would likely summarize their relationship as is. I personally don't see them ever fully making up and being friends again, but the relationship could somewhat be restored through the events of the episode. I think it would be more mature a route, however, for the two to realize they can never really be friends again and learn to just go their separate ways and get on with their lives. I dunno, would that work for this show?
So that's my take on the matter, what about you?