Personally I think Gilda would have been a great character, acting much like Rainbow Dash (Who is quite popular), but she just had anger issues which made her different from Dash. Personally I agree that Pinkie was being selfish, but not a bit selfish, straight-out selfish. She was very wrong to do that, and actually now that I have been informed about this and really paying attention to Pinkie's characteristics I kinda... don't take a liking to her as much as the others.
But back on the topic about Gilda. She, like I said before, would have been a great character, yet Pinkie got her blood to boil, and she eventually took it out on almost everypony she was around. Dash was very rude at the end to me, because instead of asking why her friend had yelled at Pinkie and why she had acted like this, she just told her to leave and find a new friends. Yeah, Gilda was self-centered, but Dash can be like her a times as well.