rowe,
Everybody's advice is good. Think about it.
Although you are right to want more for your dsd than you had for yourself you cannot impose that on her.
You cannot make her want it herself.
The only thing you can do is guide her.
Negotiate. Make a friend of her. Give her something to look forward to by helping her to make great plans for herself...plans that will motivate her.
As everyone says, it is unrealistic to ban boyfriends totally.
If the boyfriend is a twat, trust her to find that out for herself. Tell her you think he's a mistake but it's up to her as long as she continues her studies.
Make her FEEL the weight of the responsibility on her own shoulders. And be there to pick up the pieces.
Can you work out some sensible strategies, that your dh might agree to and that you can act on together?
You might have to give up some control - be aware of that (- it's quite liberating actually!!!)