I think there's a lot children 'learn' at nursery without being aware of it - stuff like sharing, taking turns etc as well as just general socialising with other children (not suggesting at all that your DD doesn't already socialise with other children ). If it is a nursery attached to a primary school I would imagine it is only half days - but 5 days a week...our nursery is 2.5 hours a day, either morning or afternoon sessions, with preference given to siblings of children in the primary school for the am session.
Our nursery has had issues with parents taking their children out for extended periods during term-time, primarily because it makes the child has to then effectively settle in again when they come back which can be difficult. Also, state nursery places can be very over-subscribed so you might be taking a place from another child who would attend every day.
If you are unsure, why not look at some privately run pre-schools in your area. Once your DD is 3, she gets funding anyway, so you wouldn't have to pay the full cost and private nurseries/pre-schools have more flexibility on attendance, eg your DD could go 2-3 mornings a week, instead of every day.
Either way, I would certainly recommend some form of pre-school before starting in reception - as SoupDragon says, it definitely makes school less daunting.