Hi S.,
My son was 2 1/2 when my daughter was born almost a year ago. Shortly after her birth, we moved to a new house where they have to share a room, so I have some similar experiences.
First, regarding nursing during the day -- is there a place where your daughter will play with her toys, since you are moving them? Her room, or a playroom? -- I would put a rocker or chair of some sort in there if it fits and nurse in there. If no chair fits, just sit on the floor and nurse (with your back to the wall for support -- and a boppy helps, too). That way, you can closely monitor your daugher while you nurse. With my son, nursing was always ideal -- with my daughter I had to nurse wherever and whenever and found myself nursing in places I NEVER thought I would, lol! -- Frequently in the drivers' seat of the car at a store parking lot, lol! Got really good at it though!
At 3 1/2 -- are there some local classes/camps your daughter can take this summer? For example, we go to the local YMCA 2x/week -- my son takes a fun gym class from 8:30 until 10am, my daughter goes to the nursery and I work out and shower -- then I go play with my daughter until my son's class is over. As yours would be a newborn (and you will be tired) -- you could go home (or at least to your car) and sleep for a while. Unfortunately, at age 2, I did not have that option with my son (no classes for 2 yrs) -- good thing my daughter was a good sleeper (only woke a couple of times/night). For sleep, I just went to bed when the kids did -- no hubby time, unfortunately, TOO TIRED. He just had to cope, but then he's an adult, most of the time anyway. ;-) Of course in the fall, your daughter will be in preschool (or 4 yr. kindergarten in some places), so that may help give you and the baby some alone time, too.
Regarding the room -- yes, I'd have her go to the store with you to pick out new bedding, etc. -- then explain that you will fix up her room for her while she is away. That said, six weeks sounds like a very long time -- what is it that you cannot get done with her around? Could grandma and grandpa come to visit you instead? I would think that it might be a bit strange for her to be gone for so long, only to come home to a new baby...
Finally, I'm sort of assuming you've discussed the new baby with your daughter? At 3, except in the case of a developmental delay, she should be able to understand the concept of a new baby and "help" you prepare -- make her part of the whole process and she will feel more in control of what is happening. This is VERY IMPORTANT. It is when preschoolers (and, well, all of us for that matter) feel totally out of control that they start to react in negative ways.
I sure hope this helps. Good luck with everything and congratulations. This is an exciting and wonderful time!!
Angie