You are very angry at your MIL for withholding information about your husband's family. I don't blame you, but she was probably in denial that it could affect your baby, just as your husband is now.
Both you and your husband contributed to your daughter's chromosomal makeup. Did your doctor specify that your daughter's incomplete Chromosome 8 came from your husband? Did your doctor tell you that autism could be detected in utero, or that it is caused by her chromosomal abnormality? That research is speculative, at best, I believe.
Finally, had you known the genetic risks in your husband's family, would you have chosen to never have children since not all disabilities can be detected in utero?