I've arrived in the evening and found lines for the HSR shuttle to be at least 10+ buses worth long, and other times found no line, so there is a chance there won't be a line for the shuttle, and a chance it will be brutal. Does your friend speak mandarin?

I would say they have the following options:

1. take the airport metro line to the Taoyuan HSR station
2. take Uber or a taxi to the HSR station
3. don't fret and just overnight at the Novatel (higher cost) or Holiday Inn Express (lower cost, but requires uber or bus transfer)