Seems like I pissed off Uesugi Kenshin (上杉謙信) by attacking too many "innocent" houses (well geez, it's a strategy game, calm down will you?) and she declared war on me.
Fine, usually I'd just finish up the current war then deal with her armies, but whenever she's leading a unit on the other side, I get quite a beating instead. This way, even the first part of the "plan" proves to be getting harder and way too costly in terms of manpower, money and time.
Is there a way to beat her, or at least stall the advance? Did I expand too quickly?