Not a lawfag or a medfag, but this is what I got from the oral arguments.
RBG seems to be lucid, her questioning seems on point to the facts in the case.
I did hear some pauses in her speaking, which makes me wonder if she is still having some trouble breathing or issues with lung capacity.
The pauses in her speaking may also be attributed to natural aging or perhaps a slight difficulty in selecting words to complete a thought.
Nothing big, but obviously the questions regarding her health remain.
The judge in the Epstein case was also in advanced years, so who knows just how long RBG can hang on.