I would do the same steps as above.
If fuses look good and disconnecting the battery doesnt work. I would contact the dealer and basically play stupid and tell them your fuel guage level isnt working. Dont tell them anything about you jumping your sisters car cause im sure they will come up with some b.s and tell you
"uhh, you just voided warranty because you shorted this or that out "

hopefully disconnecting the battery will work since that will reset the ECU.
I would suggest pulling out the main fuser but im not sure which fuse it is.