Re her reaction, a lot depend on where the conference centre is and when she found out about her father's death.
I work for one of the professional services firms, and at one point lead part of our training function. So I'm envisaging how it would happen on one of our courses.
Ours are always in the middle of rural nowhere, with no public transport and taxis that stop running after 8pm. When we organise evenings off-site we have coached booked months in advance for that very reason.
And in terms of timetable, we generally finish lectures at around 6pm and start dinner at around 8pm - giving people a couple of hours to relax, call home, use the gym or do some work. So on one of our courses if someone referred to something happening as during drinks after dinner they would certainly mean after 10pm.
We cater at one bottle of wine between 4 people at dinner. Possibly also a drink on the firm before dinner, but paying for own drinks after dinner.
So, to me, is sounds entirely possible that at the time Beth found out about her father's death she was unable to drive legally, or travel by public transport, or get a taxi for any price. And that's leaving aside the issues about driving for 3 hours after hearing awful news. I recall one occasion in the past when we couldn't get a delegate home until the following morning when his wife thought she was miscarrying at 2am, and believe me I spent hours trying to find a solution. The firm would have readily paid for a taxi for him if we could have found one that would come.
As for what happened in her room, only you can decide what you choose to believe. Those of us who have said we'd be OK with it have been told we're polyannaish, which I find a bit off. For me, the main reasons for believing his story are that the basic scenario fits with my experience of attending and running courses, he told you himself readily, and because I don't place the same amount of 'sexual weight' on beds/nighttime/drinks that others seem to - if people are going to cheat then, IME, they'll find a way to do it no matter what. I don't think that's particularly pollyannaish, and neither is it a dig at people who feel the other way.
I hope it all works out.