Always use the wall plug for recharging, only use USB to buy or delete books, and then unplug it. At least the charger has a nice looooong cord, so can plug her in and read in a book some distance away.
Interesting thing about the charge indicator. After the upgrade, it only went about 1200 page-turns before it dropped one bar. I just kept going, and now it is down to just two bars, and it has stayed there so far about another 800 page-turns. I am going to wait until it gets down to one bar before recharging, but at this rate, it may never reach that.
It never stayed that way so long before. I have not done a soft reset yet, but will wait to see what happens before doing so.