I have brought the issue up and - after the initial shock - it was self-decided that she would learn to swim or sink. In context, I know she will be fine once her feet are found; I should not have prolonged the affair as I did but it's done now (still friends, but not symbiotic*).
As I do not know how to address specific quotes, I will address specific posters -
Black Sheep:
Both. At first, I felt bringing it up would cause her to become more emotionally unstable instead of inducing a reality-check, resulting in me having to cut off communication entirely. Thankfully this didn't have to happen and each of us learnt something.
acd:
Your last three lines struck home with me and helped me zoom out a bit; ultimately we are responsible for ourselves and cannot, should not, rely on others to dig us out of the holes we throw ourselves into. In order to grow into something beautiful, we must be willing to get dirty. I predict that she and I will be fine - strained for a time - but better for it.
Flavus Aquila:
Aye, this is a lesson I am trying to learn. Looking back, I am amused at myself for thinking I could change others for the better; people will change for themselves and precious few others.
Lerxst:
I would not ascribe this to all INFJs, really. I imagine with age comes the wisdom to know what can and cannot be changed, and I am (terribly) young. The personality type system is useful for discerning general traits but beyond that, it's not very useful in my humble opinion. Hope I didn't take your post out of context ~.-
Kiu:
This is what I did, more or less, and it worked! It seems dancing around the shrubbery isn't always the best idea when picking berries.
K-gal:
I will contemplate your advice on healing and empowerment, I haven't thought of it like that before. I have been slowly withdrawing myself from her and she has noticed, and some awkwardness has ensued - perhaps something will come of it. Regardless of where it goes, I believe she will be fine and I just need to make more (quality) friends.
Corndogman:
I would tell her to take a hike if there wasn't another option; otherwise, I'd prefer to settle the matter differently.
Korena18:
Yes, very much

Having to step back and take a breath was essential. I must frequently remind myself (I am 17 years old and slightly dramatic) that the world does not start and stop on a dime-toss, that the latest emotional crisis (mine or others') will likely not seem nearly so important 30 minutes from now, nor will many others care. To quote Slaughterhouse Five by Kurt Vonnegut, "And so it goes."
NDN NT:
You phrase it much better than I could have - this was the hardest thing to come to terms with during this ordeal. Learning to curb the...zeal to create a perfect world for someone else is going to be a rough ride, I think. Rough but necessary. It's taken multiples tries but I finally got it (I hope): clear boundaries are extremely important in any kind of relationship, or all kinds of swamp will encroach on your house.
AhSver:
Ah, my apologies for the mix-up. She is/was an output, but not for caring necessarily. I just wanted someone to hang out with to assuage loneliness; unfortunately, it took a wrong turn when I did start caring and she was the only outlet.
gps:
Quite right. Had I known what I symbiotic relationship was, I'd have labelled it such. We both get something for something else, leaving both parties to blame for any issues that spring forth - I have accepted this some time ago, just did not know how to deal with it, I suppose (?). By accepting blame for unintentionally praising her self-defeatist behavior, I also resolved to untangle myself from her to promote self-sufficient behavior (if not with my loss, then through that of a multitude of others). As for harmony: I had hoped to banish her fears for her so she may find peace in herself, but I can see now that it isn't possible - only she can do that. Any "harmony" resulting from that path would've ended in something very nasty. I will do my best to do this --> "Reward the behavior you want to promote. Try to ignore the behavior you wish to demote", thank you (the other two aren't an option, unfortunately).
Dragon:
I believe it is unhealthy because she is emotionally exhaustive to me and I allow her negative behavior to flourish unchecked. A certain distance will be maintained from this point forward, yes.
To everyone:
My sincere thanks, I am deeply grateful that anyone would take time from their schedule to help a faceless unknown over teh mighty Interwebz. I hope that I am able to repay the favor during my stay on the forum (I rather like it here)
*Thank you for the new terminology; I am a high-school student and delighted to find something that describes this.