Sorry to read this experience. Like others my experience has been the change of airport was highlighted when searching flights so never select such flights.
I am more surprised that your friend had to collect and take her luggage between the two airports? Is that correct? Most definitely I would ask for a refund of the baggage fee. One reservation so luggage should be tagged to the final destination.
Goodness me even when I fly back to the USA and have to collect my luggage to clear customs and then put the bag on the recheck luggage belt I do not pay again (well I am 1K so issue is somewhat moot, but they are not collecting fees from non'elites).