I'm a teacher with an AS son, and other members of the family tick many boxes on the spectrum.
Your SIL is a busybody who is doing no one any favours, herself included.
'She's pretty sure your DD is autistic?' On those grounds? My son has never tippy-toed in his life. More of a hulk type persona.
Trust me, if she was at 5, you'd have picked up on a lot more odd quirks and pointers by now.
That old saying 'A little knowledge is a dangerous thing' really applies here.
Have a list to calm you down, others on the sn board have found it relevant.
Asperger's Syndrome
Main characteristics
Difficulties with social relationships.
Not picking up signals and info that NTs take for granted such as facial expressions, intonation and inferred information.
Difficulties with communication.
May speak fluently but take little notice of reactions, may monologue, may not be aware of audience's feelings or reactions.
May be over-precise, formal or literal in speech. Jokes, metaphors, sayings, figurative language may cause total confusion, stress, meltdowns etc.
Difficulties with social imagination, imaginative play and flexible thinking.
This one causes some confusion as people say 'Well, he plays with his lego and makes up stories and has imagination, so...?'
It's the social aspect of imaginative play that can cause difficulties. If the child is in total control of their 'world' and setting the agenda, then they are being imaginative. AS children find it difficult to play when other individuals are involved that have different ideas or who don't perform as expected, unlike a lego or toy figure.
Abstract thinking is another area of difficulty, although the child may learn facts and figures easily, dealing with abstract concepts, without clear outcomes may be a challenge. Subjects like literature, religion and philosophy.
They may also be:
socially awkward and clumsy in social relationships with others
naive and gullible, a good rule of thumb is that many Aspies function at an emotional age 2/3 that of their chronological age.
unaware of how others feel
unable to carry on a 'give and take' conversation
upset by any change in routines and transitions, often undetectable to NTs
literal in speech and understanding
overly sensitive to lights, noise, odours, tastes and tactile sensations again often undetectable by NTs
have fixed interests or obsessions
physically awkward in sports, often those that require simultaneous application of different skills.
Not a team player in any sense.
Possibly
have an unusually accurate memory for details
sleeping or eating issues that cause problems
trouble understanding and processing things they have heard or read
Inappropriate facial expressions or body language
unusual speech patterns, repetitive or irrelevant remarks
stilted, formal speech
overly loud, high or monotonous voice
stims that may involve rocking, fidgeting, joint cracking, humming, pacing...
Still think she's got a point? Or is she just an annoying 'expert'
God help you if her next course is on Exotic Tropical Diseases and parasites.