Teenage child was diagnosed with the autism. We are asking for the advice

This is puzzling. I might suggest starting with getting the home properly assessed for VOCs, formaldehyde, seemingly harmless spores and moulds which are invisible and might only cause reactions with individuals allergic to them. It's a little expense but can put a great deal of ease in the long-run. If there are traces of anything it could be worth investing into an air purifier for her room. 

Anxiety is always a secondary response, never the problem. It's a signal that there is a problem and part of our hard-wired fight/flight mode. In modern society, it is constantly setting off like an alarm. Something harmful is happening, find, create, make protection.

You mentioned seeing a paediatrician, but has she had an MRI? If not, I would book one. It might be good to get blood work as well. I experience something like anxiety when my blood pressure is low. I just need something with salt and an orange. I supplement my diet with high-mineral content spring water. There could be a few issues. Allergies can arise out of nowhere. Suddenly we cannot digest a thing or suddenly we start fainting. We can be allergic to formaldehyde or various compounds in the air can cause dizziness and headaches. Obviously if it's the whole house, one can check the carbon monoxide. But if it's one human, it could be an allergy to carpet underlay or paint still off-gassing several years later. These are human symptoms which are communicating something is amiss and needs a practical fix. 

of course she won't feel safe when something arrests her physiological being. It's proven to happen on repeat - with out warning. She doesn't trust the body she's trapped in as it feels like the mechanics are faulty and she cannot fix it, this invisible cruelty cannot be apprehended. It can hurt her at whim. That would cause anyone anxiety.

Does she have a garden she can play in? Can you at least find a routine to keep her healthy? Yoga, judo or ballet? She's having physical issues, so I would help her learn breathing technics and core strengthening, stretching exercises which are slow, fluid and not jolting. She needs something she can control. And possibly something of interest she can excel at. 

This is puzzling. I might suggest starting with getting the home properly assessed for VOCs, formaldehyde, seemingly harmless spores and moulds which are invisible and might only cause reactions with individuals allergic to them. It's a little expense but can put a great deal of ease in the long-run. If there are traces of anything it could be worth investing into an air purifier for her room. 

Anxiety is always a secondary response, never the problem. It's a signal that there is a problem and part of our hard-wired fight/flight mode. In modern society, it is constantly setting off like an alarm. Something harmful is happening, find, create, make protection.

You mentioned seeing a paediatrician, but has she had an MRI? If not, I would book one. It might be good to get blood work as well. I experience something like anxiety when my blood pressure is low. I just need something with salt and an orange. I supplement my diet with high-mineral content spring water. There could be a few issues. Allergies can arise out of nowhere. Suddenly we cannot digest a thing or suddenly we start fainting. We can be allergic to formaldehyde or various compounds in the air can cause dizziness and headaches. Obviously if it's the whole house, one can check the carbon monoxide. But if it's one human, it could be an allergy to carpet underlay or paint still off-gassing several years later. These are human symptoms which are communicating something is amiss and needs a practical fix. 

of course she won't feel safe when something arrests her physiological being. It's proven to happen on repeat - with out warning. She doesn't trust the body she's trapped in as it feels like the mechanics are faulty and she cannot fix it, this invisible cruelty cannot be apprehended. It can hurt her at whim. That would cause anyone anxiety.

Does she have a garden she can play in? Can you at least find a routine to keep her healthy? Yoga, judo or ballet? She's having physical issues, so I would help her learn breathing technics and core strengthening, stretching exercises which are slow, fluid and not jolting. She needs something she can control. And possibly something of interest she can excel at. 

Just a side note: While there is a glorious amount of help here for learning about autistic wiring, the first port of call should always be making sure the environment she's in isn't harmful and ensuring her health and safety, which can fix anxiety. 

But we are hyper-sensory to our environments. We don't have the same sort of defence mechanisms NeuroTypical individuals have to dull their senses. With enough education and discipline and practice, Autistic senses can be as good or better than hard-wried tools for calculation. We can learn to identify frequencies and spectrums, we can learn to identify chemical particulates seemingly invisible to the naked eye. We can learn to identify smells, compounds, tastes, palettes, weather patterns, and so on. This is an incredible ability in a tribal setting for early humans. The modern assault on our senses, though, is dangerous for us. We are not capable of dulling these senses and often this also means being vulnerable to these elements, might mean we have severe allergies and intolerances. While too much vitamin D can give anyone migraines, ours can be from so many things we can sense and calculate. But when young, we need natural, healthy, safe environments like young potted seedlings. It can take a long time to learn how a weakness can actually be a strength or a malfunction is actually our ability to assess a toxic environment.