I think it is a great idea to get her in and used to it before the baby comes along. then she doesnt need to be pressured to rush into it (and neither do you). It may also be good for you to get a little bit of alone time while you are heavily preg.
I found keeping DS1 in care worked well for us, it gave me time with DS2 and also didnt disrupt himn. then on days i could keep him home or get him v early etc it was a 'bonus' for us all.
Having him at cvreche also meant he wasnt stuvck at home in the early days when DS2 was asleep all the time - and i could get to appts etc that i needed to more easily. he also loves it so it was a win:win for us.
and NO the guilt and wistfulness NEVER goes away!!!