What would happen if her UTI wasn't treatable? Would it end her in the end? Does UTI bacteria spread? What will happen with this otherwise simple bacterial infection?
Sorry, I'm not the right guy to answer these questions. And it's late :) But given how "normal" drug-resistant bacteria work, someone with just an UTI alone (even if untreatable ) probably wouldn't kill a healthy person. Eventually her immune system would prevail and either eradicate the bug or restore an equilibrium where the bug is still present but not causing any serious problems. People can have chronic infections that don't go away but don't kill them either.
What you're really worried about are people like OP (immunocompromised people) and the fact that such a super-bug could spread, share its secret with other, less harmful bugs and one day become so common that every patient runs the risk of getting it.
At that point you'd have to worry each time you do even minor surgery because if such a super-bug would enter your patient's wound, it would cause general sepsis and you could do nothing but watch your patient die.
And you'd have to worry about highly infectious and once-deadly diseases like tuberculosis to also acquire these super-resistancies and become untreatable again. You might end up with entire hospitals dedicated to ease the suffering of those who can't be helped anymore. Just like it was before antibiotics were discovered and became widely availabe.
Well, that's my idea anyway. Again, I'm not the best guy to ask this, but I've seen some pretty informed and down-to-earth doctors get pretty gloomy and scared when talking about this, so it's definitely reason for concern.
What are the antiobiotics?
the article you linked talked about a woman who got infected with bacteria that produced NDM-1. That's an enzyme that allows them to render most of our commonly used antibiotics harmless and thus far only found in patients who contracted it on the indian sub-continent (NDM actually stands for New Dehli metallo-beta-lactamase). This type of bacteria is usually still resistant to at least two antibiotics: Tigecylin and Colistin. But in this particular case it seems even Colistin wasn't working. Scary stuff indeed.
Could those nastier, but effective antibiotics be administered the same way to ensure the patient is cured? Or are they nasty to a level that no special treatment with administration helps?
We're not talking about some kind of mythical poision here that only a selected few can survive. Some people will tolerate it just fine, others won't - just as it is with pretty much any medication. The route of administration may vary, but it isn't really the issue here.
It's just that until recently doctors chose to use this class of antibiotics, and they did so almost exclusively in really, really serious cases where side-effects didn't really matter. Now they're increasingly forced to employ these measures even in cases where they used to have a wide variety of different antibiotics to choose from.
And there are people who're allergic to certain antibioitics, pregnant women who can't take certain antibiotics because they're dangerous to the foetus, young children who can't take some antibiotics that affect their development, sick people who can't take certain antibiotics because their of interactions with other medication... There are a lot of reasons why people might not be able to take a certain antibiotic.
The less antibiotics there are to choose from for any given condition, the more frequent it becomes that people end up with something that is untreatable, at least in their particular case. And once you're forced to always use your super-powerful reserve antibiotics even for common infections, it's just a matter of time before more and more bugs become resistant to those remaining antibiotics as well.
So it isn't really a matter of "oh no, we can't use nukes against them, it's too dangerous!" but mostly a matter of "oh shit, we've only a few nukes left and they're still coming..."