I'm sure you are very sensitive to possible signs because of your son! The behaviors you describe could be potential signs, but could also easily be typical of any child under certain circumstances. I'm sure you're familiar with the criteria, but just to help you categorize the types of behaviors you are worried about:
Broadly speaking, children with autism are affected in all three of the following areas of development:
1. Impaired Communication - noticeable delay or absence of spoken language; or if speech is present, atypical use of language (such stereotyped or scripted speech), impaired comprehension, and/or infrequent inititaion of speech
2. Impaired Social Skills - could include lack of shared attention or reciprocity, solitary play, difficulty initiating conversation, lack of imaginative play
3. Atypical, stereotyped, or repetitive behaviors - such as rocking, flapping, using toys in non-functional ways like lining them up or spinning them
From my experience, the majority also display abnormal responses to sensory input (lights, sound, touch) and atypical patterns of motor development (low muscle tone or near spaticity, coordination issues, fine motor delays).
VERY generally speaking, children who exhibit atypical play behaviors and impaired social skills BUT have normal or nearly normal language function would be suspect for Asperger's syndrome.
If you think your daughter's behaviors might fall under the above categories, or if you feel her behaviors are detrimental to her overall functioning, it's best to just ease your mind by having her evaluated. You should find a developmental pediatrician who specializes in ASD for an assessment (a multidisciplanary evaluation including a pediatrician, a child neurologist, a child psychologist, and a speech therapist is ideal). Depending on where you live, you can look into your local school district for assessment and other services through early childhood programs.
Don't be afraid and yes it is possible.