Step-parent of undiagnosed toddler

Hi there, I joined this community hoping to gain some help or guidance. My step daughter recently turned 3 and we are awaiting an official diagnosis. Her biological mother, auntie, uncle, grandmother and cousins are all ASD. She shows a lot of traits and we are certain she is also ASD but as I said we’re awaiting an official diagnosis.

Her eating has progressively gotten worse over time. She will now only eat 2-3 foods and they have to be served in exactly the same way each time or she ends up having a meltdown. She is non-verbal still but has started to attempt some basic words and repeat them back to us so we are hopeful she will progress with this. She is very constipated and general will only do number 2 every few days and seems to be in pain when she does. She regularly suffers bad nappy rash and becomes sick with cold/flu symptoms quite frequently. We recently moved house and her behaviour has had a dramatic turn in terms of tantrums and meltdowns. Her meltdowns usually involve throwing things/being destructive, stopping breathing and/or crying and screaming until she is almost throwing up. Recently she has started hitting the sides of her head too. 

I’m just wondering if there’s anything we can do to help her cope, or to manage in these situations. Any guidance or advice would be really appreciated as neither myself or husband have any experience with this.