Seriously, all capitains of Starfleet we know, screwed up at one point or another of their mission.
As for the Admiral's promotion, if I remember, one was offered to Kirk but he chose to refuse it to keep commanding his own vessel and to remain independent. Picard
have also been offered also a promotion but certainly refused it for the same reason than Kirk. Sisko chose another fate. As for Janeway, well, we know that she was promoted to the admiralty and assigned to Starfleet Command but we really don't if it was immediately after her return from the Delta Quadrant and even if it was, she accomplished more in 7 years - where she and her crew were stranded in an unknown and hostile quadrant - more than most captains and even, some admirals, have lived in a career. Of course, mistakes she has committed during this long journey but she brought her crew and her ship safe and sound despite some losses, but a better knowledge of the Delta Quadrant and Borgs too and some alliances with new species.
I trully think that it's all these parameters which convinced Admirals to offer her this promotion (that and the guarantee that she won't lose her ship and her crew again

) and after 7 years far from her family she is very close (her sister, Phoebe, and her mother, Gretchen -> cf Jeri Taylor's Mosaic), it seems normal to see her trying to settle in and sober up, in staying on Earth as seeing as nothing could top what she lived in Delta Quadrant!
Plus, if Chakotay, Seven or even the Doctor needs her (sorry but I still don't buy the idea of the Federation pardonning and rehabilitating easily the ex-Maquis leader and the mistrust regarding Seven, the still half-Borg young lady, would take some time before fading totally away. As for the Doctor, I see him keep fighting to see his rights to exist as a sentient hologram recognized), it would be easier to protect them in an Admiral's position than if she is a capitain always in mission somewhere in space.