{{{{{{{{{{HUGS}}}}}}}}}}}}}} to you Louise, that must be so hard for you.
My first thought was, are you sure this is the right place for your lo? Have you the choice of any other nurseries/childcare options? The reason is that it is their obligation to do with Mia what you specify, does it sound like they are willing to do this? (I'm just asking b/c of the 45 min nap comment). If you explain to them how hard you are working on your naps, and how 45 mins is not enough for her, what do you think their reaction would be? If they are understanding, and will try to help, great, but, if not, it might be worth looking for somewhere else (easier said than done, I know).
Having said that, if you have no other options, I don't see that it's the end of the world. If Mia is only going in for 2 days, even if they totally mess up her nap routine initially, you should be able to keep her on track for the rest of the week, although it will be slightly more difficult in the beginning. I thought the idea of getting to know one of the other Mums who uses the nursery is a great one. Maybe you should go back there a few more times to set your mind at rest?
Please don't feel guilty. You are only human, and cannot be in two places at once
. Your lo will probably thrive at nursery, and just think of all the socialising she will be doing there, that's really good for them at this age, and will stand her in good stead for the future.