Is an explicit, verbal response that directly expresses anger always the wrong choice?
Not always. It can occasionally be the right choice for dealing with very problematic people who seriously violate proper boundaries in ways that are potentially very harmful -- assuming you have no desire for any kind of relationship with that person, ever. But even then, if you feel you must use profanity, keep it low-key. Be a gentleman. Even if the culprit is a scoundrel, don't stoop to their level. Just be firm and express your thoughts clearly, so there is no chance of misunderstanding.
In other words, if the relationship is expendable and you are reacting to a truly grievous affront, then by all means: telling them off with choice words may help re-establish proper boundaries. It might get their attention and give them something serious to think about.
However, it isn't at all wise to use the language illustrated in your examples, for dealing with problems with people about whom you care very much. I stress this, despite the fact that I'm well aware how many people are generally in the habit of talking to one another in that manner. It's quite common, really. And it isn't as harmless as it appears on the surface.
Treat everyone with respect at all times, if possible. But that goes doubly for the friends and family you can't bear to lose. If you stop to think about it, saying:
Well @#$% you then.
...is equivalent to saying, "Die! I hate you!" Verbal abuse is as hurtful as physical blows. Such statements wound the heart. And they end up harming all involved, even the speaker / writer of such sentiments.
This too, is an inappropriate way to treat someone whose friendship you value:
You don't get to just @#$%ing walk back into peoples' lives whenever you feel like it.
...is equivalent to saying, "My feelings are more important than yours."
If you value someone's friendship, regardless of how annoying they can be, you must accept them as they are, and deal with it somehow.
You did the right thing the first time, when you attempted to talk to her about how her emotional problems affect you. But try to understand that she may have emotional issues that she isn't ready to talk about just yet. That's why she pretended nothing happened.
When you confront her in a caring, respectful fashion, and she reacts by withdrawing (ignoring you), just think of that as her giving you some vacation time away from her problems.
She later returned, when after thinking it over she realized you really were trying to build rather than tear down your friendship. So at that point you should observe her behavior to see how much effort she is putting into being a better friend. You may find you need to discuss things with her less frequently, as time goes on.
Apparently emotional problems are the reasons for her heavy drinking and inability to trust people, in the first place. So you need to understand that using profanity on her, as if her feelings aren't very important to you, will only hurt and cause her to withdraw, drink, and distrust even more.
You should try a different approach this time: Be a gentleman, and let her know that you have a heart, and that you see that she is unhappy about something that she may not care to talk about.
Tell her that you respect her privacy, and that you understand some of her behaviors (be specific if necessary, in other words if she asks for examples) are possible indications of depression or some other problems which you might not be able to help her with. And while you respect personal boundaries, you wish to remain friends.
That means you will have to be very tolerant of her faults, and she may test your patience. You have to ask yourself periodically: is our friendship worth the trouble? If it is, be a gentleman about the way you treat and talk to her -- regardless.
If it is not, then it's time to move on. Just consider the fact that when ending friendships, there rarely is any turning back. If you're very diplomatic, you might be able to stay on speaking terms, at least. But you probably will never be friends again.
And if being a gentleman and graduating into maturity alienates your friends, guess what? You'll either find better friends, or they will someday wake up and recognize you for the trail-blazing leader you've become.