My 8 year old has autism. My 5 year old is fine. Early intervention did monitor my 5 year old closely until he was 4 but he showed no signs of any neurological impairment so was discharged. Having one child with autism does give an ever so slightly increased risk of siblings also having it but it most certainly doesn't mean they will. If you have concerns about you other child take her to your doctor and ask for a developmental evaluation for her.
Also my daughter will turn 2 in 2 months and all she can say are names nd thats it and if she tries to talk you cant understand her!