Depends on which culture you'd like to immerse yourself. Theres a good chance that, whatever country you choose for your sister, she will stay at after college. Unless she completely rejects the lifestyle in tw which isn't all that bad. Or perhaps its a matter of wanting to earn USD or TWD after college
One last thing to consider is that you can always do foreign exchange classes. So if you are leaning toward US-based college, there is a chance of enrolling in 6-12 months foreign exchange classes at the very college she got accepted into.
Heck, if you want to be even more creative, sign her up for a session of the Loveboat tour