I'm guessing from the first panel (using what little Japanese I know) Hartmann is probably referring to the comic where she was trying to use Perrine as an electrical generator since she mentions something like "an experiment" and "using magic" and "power generator". As to why Ursula is pissed off I'm guessing its either A) Erica be trolling (as said before) or B) Erica actually made some sort of scientific discovery/breakthrough that Ursula was trying to solve (and thus was trolled)
Leave it to Lieutenant Hartman!! (Little Sister Take)Yearning, and jealousyxx day xx month
A mail arrived from my sisterAHAHAHAHAHAI'm sick of these SistersI’d never win against her anyway!!!Ursula is boiled downWith it is the detailed plan of an electric generator utilizing a peculiar magic that she devised
