I think you are on the right track. Your DD's sensory issues and delays may well be attributed to the flu shot you received during your pregnancy. I also have a flu shot baby, DS #2 who is now 5. I also remember an excessive amount of hiccups when he was a baby! Don't know if there is any connection there, though. DS #1 was very bright and hit his milestones early. He was very outgoing, and was an early talker, too. DS #2 had a speech delay, a fine motor delay, some OCD tendencies, and sensory issues (wouldn't "hear" us when we said his name, easily overstimulated in busy environments, super high pain tolerance, ect.) The flu shot contained the full 25mcg mercury, and after doing some research on the stuff, I am convinced that it was the main culprit. Even the ACOG tells women not to eat certain kinds of fish because of the mercury risk, and yet they have no problem with it in a flu shot?
I have also run across other moms (3-4 at least) with a similar experience: they have a child with sensory issues or a speech delay, and come to think of it, they also had a flu shot during the pregnancy. My DS #1 and #3 are typically developing, and I did not get any shots during their pregnancies. It is only anecdotal evidence, but that may be all we get. It's not as if the CDC wants to find that connection.
On the other hand, many of the flu shots this year are mercury free, which is very good news! Personally, I will never get the flu shot again. However, if I did, I would choose mercury free.
Best wishes for a healthy baby!