Stimming makes me cry

Feeding Alanna breakfast ended with me in tears. No matter what I did, how many times I called her name, tickled her, squeezed her hand, played airplane with the spoon, etc.... she would not make eye contact and she would not stop stimming. Hitting herself in the head, growling, hitting herself under the chin, flapping her hands, staring out of the corner of her eyes at her hand.
Let me rewind to Gotcha Day. When they handed her to me, she would not look at me, she simply diverted her eyes up, to the side, etc... anywhere except to me. She hit herself in the head and growled. "She's acting like she's autistic" I thought in my head. It scared me, I'm not going to lye. And as Serge asked me if we wanted to adopt her, I said yes, with a huge smile, when in my mind I was thinking, "I don't know, is she in there?" Maybe that behavior is normal for a 16 month old with Down Syndrome.
Whew, this is hard to type about the child I love so dearly, the child I can barely stand to be away from for several hours, the child who rarely ever sits in a stroller because I love to carry her around in my arms, close to me.
That night I layed in bed, exhausted from the crazy ride to our region and our 10 minute meeting with our new daughter. I remember thinking, I can't do this, we will just tell Serge we can't do this, we will just go home, she is so young and cute, she will get adopted by another family for sure, a family more equipped to deal with autism. Why did God even lead us to adopt such a young child, we wanted to adopt a 3-4 year old. We could have saved a child from being sent to the institution. I prayed and fell asleep.
The next morning I felt better, and of course after another visit with her I was in love, she made eye contact, played with toys, etc... She was still stimming and growling, but she was certainly in there. And those behaviors aren't unusual for a child who has spent their lives in an orphanage with no stimulation.
The stimming seemed to get better for awhile not as much hitting herself in the head, when we met her she had rough spots on her head from hitting herself so much. But she has added more stimming behaviors that we didn't see before.
She hits herself under her chin with the tips of her fingers
She flaps her fingers
She smacks herself hard in the face, I hear this when she wakes up in the morning and when she is trying to go to sleep at night
She rocks violently back and forth in her exersaucer
She never used to stim violently when I layed her down to bed. Now she does, and she sits up and rocks and hits her head on the crib, and she gets up on all fours and rocks really hard back and forth. I liked it much more when she layed there and sucked her thumb till she fell asleep. I just recently discovered she was stimming to go to sleep. From now on I will be holding her till she goes to sleep then laying her down.
It took a long time for her to respond to her name, but not only her name and sound being made would not make her turn. Yes, we do have a hearing test scheduled.
Now she does turn once in a while when we say her name. Sometimes not at all and sometimes only after we say it a couple times.
She is smart. She will not clap on her own, but she will pick up my hands and put them together so I will clap. She plays Peek-a-Boo, but she has no reaction to it, but I assume she likes it, because she puts things like birp clothes or shirts over her head to play. She never laughs in response to something, only to things physical like tickling.
I'm describing all this so I can input from other parents.

When we take her places, of course the stimming gets worse, because there's so much more going sensory input. I've noticed it makes people uncomfortable. They stare. Sometimes they ask why she is hitting herself, or growling. They will say hi but she diverts her eyes, and pull back her hand when they touch her. So they never ask to hold her. People have said things to her like "why are staring at your hand" "what are you staring at" "she must see something we don't", etc....

Yesterday was a good day, we had Drs appts to go to and she did not stim nearly as much as she usually does when we are out. But she is making up for it this morning. After feeding her breakfast I put her on the floor in the living room and I went into the kitchen to cry and to make my coffee. When I looked in on her she was rocking back and forth hitting herself over, and over, and over. I called her name, but of course she was in her own little world.
When I sat down on the couch with my coffee she crawled over and put her hands up to be picked up.
We work with her face to face for hours everyday. Playing, singing songs, doing hand motions. I have some deep massage I've been doing, which she normally does not stim through, this morning she did though.
I don't know if she's autistic. But it scares me so much, why, because I don't want her to be stuck inside herself. Noone wants their child to not respond to them.