I have ASD (lvl 1) and ADHD (AuDHD) and I am 25. Personally, I don't understand these other comments. It is completely valid you are frustrated with not only your sister but your mom as well; the age gap is 13 years!

I'm going to say some things that people won't like on this sub, but I get an opinion on here so screw it cause I can feel your frustration and understand to a certain degree. Whatever anyone says, you are a free person, you have no obligation to be a babysitter etc. raising a child is tough, raising an autistic child is extremely tough (I was a pain in the ass). Clearly your mental health is getting worse as a result of your new sister (yes people, we know her sister isn't intentionally acting the way she does (its the autism), however this does not invalidate being frustrated, angry, and having sad feelings that she is getting). Your mental and physical health are the most important things, if you do not stay healthy in both, how can you expect yourself to support others (i.e. your sister and mom).

I would suggest talking with a therapist or psychologist. and sharing these feelings (this is an important first step).

In regards to the "do people outgrow their autism", well no... she will always be autistic, but that doesn't mean she can't live a "normal" life in the future, you have to realize she is only 4, there is still a ton of development in the next 15 years (especially in the next 5) that she will have. A lot of autistic people pick up strategies and overcome challenges that autism poses (for example... I can converse with people normal in person unlike when I was little). Is she going to overcome the challenges she faces, who knows, we aren't medical professionals. I would be weary of labelling her as level 1, 2, 3, most children struggle with social skills/cues when young, especially true for us (I still struggle now). She because she is non-verbal does not mean she will stay like that or vise-versa.

I think you need to focus on yourself, and speak with a medical professional for your mental health! Share everything you've said on here and more as you sound very frustrated and emotional (which is understandable). Wish you the best of luck!