My son was referred very young for assessment. They don't tend to diagnose autism at that age where I am, but they do assessments to see the extent of delays and keep track of skills and behaviours. My son was diagnosed with Global Development Delay (GDD) at around 18 months, then he is seen and assessed by the developmental pediatrician every 3 months to check his progress. It's only over time and with thorough assessments that they can really diagnose autism - it's not the kind of thing that you get after one appointment here.
If your LO is delayed in some areas, regardless of a firm diagnosis, they can help with things like physiotherapy, OT, speech therapy (though she is a little young to know if she has difficulties with speech). At my son's first appointment when he was very young they tried to get him to engage/play with toys, make eye contact, respond to sounds/names, make sounds/babble, smiling, gesturing, etc.
My son was referred because of gross motor skill delay (no rolling and could not get himself into sitting/crawl at a year), little eye contact, not very responsive to his name, and no vocalizations at all by 18 months (other than crying). They really can change though. My son is 2 years 3 months now and has great eye contact and communicates well even though his speech is delayed. xx