If she doesn't study japanese at A-level it would be a good idea her her to do at least one modern language at A-level, English might be useful as well, the others can be her choice, preferably subjects she is likely to enjoy and do well in.
If she wants to work in Japan can she not do a degree in something she wants to do and learn Japanese anyway? University japanese is likely to be mostly examination of japanese literature, rather than conversational japanese. Doing two degrees is extremely expensive and would take a long time.