What I would do is just scale based on the info you already have. (Also, you probably should have posted in altcoins section)
You mined ~350 LTC, she claims you mined ~21800 LTC. Scale = 62.3 times as much.
So if you mined with, say, 4 cards, then you would have needed to mine with roughly 4 * 62.3 = 249 cards
If you were full on mining with, say, 300W per card, that's 1200W total. To reach her estimate you would have needed around 1200 * 62.3 = 75 kW
Of course you should calculate the numbers better, but it should be fairly easy to point out that you didn't have 249 cards, or couldn't possibly be pulling 75 kW from a cottage, etc.
Best of luck
if you want to PM for some more courtworthy evidence etc. I was mining ltc at the time might be able to get something more accurate with you