How could it be a major step forward? She was treated with standard drug therapy. I'm asking this as a genuine question as I think I'm missing something. [..]
She's had no treatment for at least a year and tests come back negative for HIV. That's a cure, which is very different to the usual effects of the standard treatment. The standard treatment suppresses the progression of infection. It doesn't cure it. The patient is still HIV+
There are a few possibilities:
1) During the 5 months in which the mother took the child somewhere for some reason, a full cure was made in some way. Magic, illegal medical experiments, whatever.
2) For some currently unknown reason, the standard drug therapy cured this specific individual and would have done so under any circumstances because of something unusual about her.
3) The standard drug therapy cured her because it was started when she was 1 day old.
The currently pencilled in hypothesis is the third one. It's thought that established HIV infections form reservoirs of infection that the standard drug treatment can't kill off but that this extremely early treatment kills the HIV off before the reservoirs are formed. If so, it might be possible to cure other people born HIV+. Maybe it would work for all people born HIV+ Maybe it will lead to a better understanding of how HIV infection progresses in humans, which might lead to more effective treatments and maybe even a general cure.
So yeah, it's a major step forward. Unless the cure was a secret magic spell or illegal medical experiment during the time the child was outside the medical system, this is proof that it is possible to cure HIV in newborn babies. That could be a big deal.