First suggestion - never panic! Even if you decide to act after school is started, it will be ok
Even if you decide to not push for acceleration, it will most likely be ok
The first day of school as well as this grade of school aren't huge brick walls that you'll never get past if you don't push them over this week.
Next, if the psychologist recommended the acceleration, I would guess your dd is well prepared and will be able to handle it. My assumption here is that the psych is local to you, so he/she knows your school district and local math curriculum, and that the psych eval included some type of achievement testing.
Re advocating at school, I'd ask the psych to either write a letter specifically addressing the need for math acceleration and supporting your dd's readiness, or ask that the same info be included in the summary report you receive from the psych evaluation.
My own personal experience re showing the WISC results is that it didn't get us very far in requesting acceleration - achievement test numbers were far more effective. I wouldn't *not* show the WISC numbers however - it did serve us as a valuable data point when school staff tried to argue against acceleration even when we had the achievement tests.
Good luck!
polarbear
ps - you might also ask how your school differentiates for kids who are capable of moving ahead in math, and whether or not there are any other students in your dd's grade who will be taking 2nd grade math. One thing I realized later than I wish I'd realized was that in elementary school, I'd get worried about asking for some things such as this, only to find out later on that there were already other students actually doing it simply because their parents pushed for it... but the school staff wasn't going to tell anyone about it unless you asked.