Depends on your dd and on the schools of course.
My general view though would be mixed all the way. I went to a good mixed comp (plenty of Oxbridge, Russell group and medical school entrants. A good number of girls taking A level physics 20 years ago). The daily experience of people of both sexes and mixed social backgrounds as normal, so seeing everyone as an individual, not a type, provided a very strong basis for understanding, mixing and working with people and a healthy basis for personal relationships in later life.
My experience of women who went to single sex schools, the many I've met at university and at work (disclaimer, I am not saying all SSS pupils are like this but my experience is many are to some degree), is that many, even most, share an unhealthy distance from, mystification and idolisation of the opposite sex. They find it harder to have men as friends, always thinking of them as actual or potential boyfriends and behaving possessively about them. They often have an exaggerated idea of sexual differences and can't recognise male bluster and bullshit for what it is, sometimes being rather credulous.
When I hear exaggerated and entrenched attitudes about sexual difference, it almost always comes from people who attended single sex schools.
I think the idea that boys are 'a distraction' gives them mystical status and actually makes them seem much more intriguing than most teenage boys really are, perhaps setting girls up to be disappointed!