You need to look back at her early childhood, can you recognise any signs then? As any ASD assessment will ask you about how she was when she was 4-5.
Sensory Processing Disorder is actually a separate diagnosis, although there's a big overlap.
Autism is a triad of impairments, being social communication, social interaction and repetitive and restrictive behaviour.
Does she have conversations, or does she talk AT you and answer your questions? Is she situationally mute ie not talking when a situation is distressing? Does she take things literally?
How is her interaction with people? Did she play with or alongside others when younger?
How is she with transitions? Did you have warn her of changes when younger otherwise she'd tantrum? Does she become almost obsessed about something, it lasts for months or years, but once she's over that it will never be spoken of again?
Was she fabulous at primary school, but would be snappy or tearful at home? And you'd put it down to tiredness or hormones but it was All The Time?
Mine is 15, I thought she was just a difficult only child for years, then very anxious and introverted, then quirky. The wheels fell off 12-15 months ago, the GP suggested autism, and everything became clear. She's no longer masking, and my eyes are open to her difficulties.