When I was in Primary school there was a girl in my class who had nothing. The Mum and step dad had just moved to our village from the former East Block. Her older sister and her would live off a yoghurt or breadroll with jam a day, I'd frequently ask her to come over and have lunch in our home because I could see she was hungry and I felt sorry.
Anyway, the parents had a new baby. Now, when I return to my parents this girl who's a good 10 years younger has everything and more you could want for. Nice house, holidays abroad, school excursions paid for, tennis, gym, etc. Her own car, hair and nails done, smoking, eating out, drinking, all that money at her disposal, etc.
Both elder sisters married very young and moved out as soon as they finished their A-Levels. It makes me so to see that clearly there was a huge difference in upbringing. I mean, her Mum got married fairly soon again, and the kids had a step dad again..the sad thing is, that he only shelled out the dosh for his own flesh and blood and the girls from a previous marriage had to go hungry while their little sister was being spoiled. At least they had each other, your dd is all alone.
Maybe you could persuade your husband to gift your older dd whatever you are allowed tax free to invest in a house or flat of her own, give her a leg up. As a mum myself I'd never stand by and let one of my kids miss out, you could still make up for it now, maybe treat her to a nice lunch and ask her how she feels about it. A willingness to listen would go a LONG way I suppose.