Is it normal that your 8 month old American pitbull female is 65 lbs?

Not really. If you got a dog from the newspaper or someone down the street's litter of pit bulls, she may very well be mix-bred. Anyhow, at 8months old, your dog is not finished growing.

She will fill out, adding another 5 to 15pounds onto her current weight. She could be a APBT/AmStaff cross, or an AmStaff, although she still may be a APBT; just she's kind of heavy for the breed; probably because her parents/ancestors were bred larger.

Most APBT SHOULD be 45-65lbs at 2yrs of age.

Just as long as she's agile and fit, she might still be an APBT, and still be great pet or working dog.