honestly I can't imagine she'd really be a 140?? How do you know?? I mean, she knew her alphabet by sight at 16 months -- talking at 6.5 months. Reading sight words at 2, and full books at 3 years, 2 months, and started chapter books the summer she turned 4.
Based on that description, I'd be surprised if her IQ were significantly lower than 140, although GooglePsychometrist indicates that the WISC-III has a time component, so if she's a slow-deep kid, that's a consideration. The WISC-III is an older test, so could be expected to overstate IQ compared to the latest revision, which works in your favor here.
I personally wouldn't expect waiting to either help or hurt.
