I used to work in a job where my regular train journey commute home was at 10.30pm. being harassed on the train by drunk men was quite a normal occurrence for me, especially at weekends and in December (office party drunks, the worst). I did learn some strategies to deal with it.
Firstly sit in a busy carriage not a quiet one. This is counter intuitive to the idea of a quiet journey, but the more people are in the carriage the less likely you are to be singled out for harassment, or for harassment to happen in the first place.
If a noisy group of drunks get into your carriage move straight away to another carriage, dont hang around and give them a chance to single you out, just go. If you can find the carriage the guard is sitting in all the better.
If you get stuck and you can't move put headphones in and start to read or play on your phone. Don't make eye contact, don't look at them, don't give them an opening.
If they do single you out be as bland and dull as possible. "Come on love, smile" "I'm tired, I've been at work all day, I don't feel like smiling". They want to get a rise out of you, don't give it to them, dont get visible upset or angry even if you're raging inside. Also don't be afraid to get up and move at this point, maybe I was lucky but I never had anyone follow me down the train.
I'm sorry your daughter had this happen to her, it's shitty that some men feel this kind of behaviour is acceptable, but they do.