I am so sorry you are going through such terrible time. Just the fact that you love your child so much and are taking such good care of her shows what a great mom you are. Thinking of you and your family.
Hugs to you. I am so sorry that you are going through this and that now you have to deal with such a wait. What if you call the local children's hospital/check their website? I would guess that they would have *someone* on staff that can do the measurements and testing required. I live in Silicon Valley, and we have five geneticists on staff at the local children's hospital (plus the perinatal diagnostic staff, which might also be able to help, since your daughter is so young still.) Since you're in a major urban area, I am sure you have some other options that can help you get a little peace of mind a little bit sooner.
I hope it turns out to just be positional flattening and the helmet corrects it. If it is hemihypertrophy, you will do a great job with it. You are doing everything you need to do for your daughter, and you will continue to do that. In the big scheme of things, a blood test every six weeks is very do-able, and you'll give her all the support she needs. We're all sending you lots of strength to get your mama mojo flowing again.
Update: Thanks, Kimberf! In my city, there is one geneticist that works at the children's hospital. She is the one w/ a 4 month wait. She happens to also be listed as one of the best geneticists in the country (probably one big reason for the long wait). Anyway, the geneticists in my area are few and far between. I found one dr. who was able to get us in last friday...we saw him and he was very "green" to say the least. He was actually googling hemihyertrophy while I was in his office. No joke. I felt like I knew more about hemihypertrophy than he did so we are continuing to push on. The good news is that we are moving to another large city in 6 weeks and this city has a really good children's hospital w/ 5 geneticists on staff. We are continuing to search for answers. Thanks for your support.