What a very exciting time.

Your daughter will love the opportunity, and won't remember the flight, even if you chartered your own private jet.

Find two flights in CW or F on redemption, and book you and your S.O in that. Then book her in economy on the same flight. For cheapest flights you could use avios for a one-way, but if the company are paying anyway...

(Of course I'm assuming your daughter has a visa to work in Japan)

If avios is a stretch, find the CW flights and book in WTP and upgrade to CW. Make sure you include a Saturday night to get the "T" fare.

I remember getting my first job. (OK it was delivering pizzas around Warrington ignore that), but after uni I recall flying out to Greece. It was great. I got a train from Exeter to LTN, via Farrington. I flew easyjet, which I remember as they let me off on the excess baggage. I really don't recall the flight itself. Or the 6 hour drive to the island afterwards.

Two days later I had an email inviting me to interview #1 for my current job. Charter flight back to the UK for that. A week later (Aug 15th I think) there was a massive earthquake (Lefkas 2003), then interview #2. That was a 24 hour ferry, a easyjet flight to gatwick, a train to a friend to overnight in Guilford, the interview in London, then I remember being shaken by tube trains at Liverpoool Street on the way to what I assume was ryanair from STN back to Rome (CIA), an overnight train (which had a sexy Austrailian lady sleeping on top of me), then a ferry from Brindisi. My mobile ran out of credit by then so I didn't find I had the job until I got back to Greece.

Then it was a ferry with a car back to Venice, drive to Calais, ferry to Dover, 2 days in a hostel while I found a flat to rent.

My point is, your daughter will be so excited about making her mark on the world you could fly her in the hold on ryanair and she wont hold it against you. Fly in First or Economy, and after 2 days in Japan you'd be hard pressed to tell the difference.

(10 years after my first job, and nearing flight #100 of the year, and I have slightly higher standards than economy to Japan, but that's due to flying long haul once or twice a month --- Economy once or twice a year is what most brits would dream of - I didn't even get my first passport stamp until I was on my second one at 27!)

Enjoy the opportunity (and the excuse for a holiday), and don't worry about the 12 hours you spend sitting on a bus to get there.