HI Albaba. I am by no means an expert - so this is just my experience and opinion - but to be honest a lot of what you've said sounds like typical toddler behaviour. DS (also 3) occasionally displays virtually every behaviour you've mentioned, and neither myself, DH or my mum (who is a teacher of 20 years standing and has dealt with many many children with behavioural issues) think there's anything wrong, over and above what's normal for a toddler.
It's probably not too helpful comparing to her twin either, I don't mean that nastily, just that children are all different and to me it doesn't sound like anything linked to her CP, apart from the fact that she may be additionally frustrated (over and above normal toddler frustration stemming from the need to be independent and communication issues) and angry sometimes that she can't move in the ways she wants to or feels she has to be forced to do physio. She's also got a direct peer to compare herself against and so might well find this difficult.
Sometimes DS has moments like you describe in physio too but generally he's pretty compliant most of the time and we can usually snap him out of a mood or potential meltdown situation with a change or toy/change of subject/distracting in some other way. But still if he's not napped or he's hungry, physio stuff never really goes well. When DH takes him he can get him to do more when DS is wavering as he's more tough on him than I am. How does she relate to the physiotherapist? A good physio should be able to keep them engaged and sense when they're getting fed up and change the game quickly to avoid scenarios where they don't want to engage. Perhaps ask to see a different physio instead of just having a break? Or switch it up, can you ask for a hydro session as a breather? Or even a change of room/environment?
DS prefers me to DH, and will often say things like 'no daddy I don't want you to read me a story, go in your bedroom' when I'm there. But if it's just the two of them they have a lovely time. Again I think it's natural for a child to have some preference between parents, it's usually the mum i think but there are always exceptions.
Oh and DS's current 'friends' are his plastic chicken from the farm, a small card with a picture of bacon on it and a small blue tray with a plastic lettuce from a playmobile set.
Of course she may have slight traits of something or other but it's difficult to discern any from what you've posted. I had a quick look online for a sort of autism checklist but a lot of them are only answerable by the child who would need to be older than 3 I think (for example 'can you easily visualise characters in books?'). If you are still worried I don't think a chat with a consultant would go amiss, I really wouldn't worry about labelling too much.
Lots of hugs. I know what you mean about it being difficult enough dealing with the disability, anything else would feel just too much. Hope this helps. 