Learn English – What she was doing here OR What was she doing here

The subject and auxiliary verb are normally switched order in a question. This process is called a subject-auxiliary inversion. That's why the auxliary verb precedes the subject in your first example.

Where am I?(NOT where I am? )

However, when the question is embedded in a sentence(or inside another clause) this process does not occur.

Can you guess [Where I am]? (NOT Can you guess where am I?)

as in its temporal sense relates to a coinciding event, something that happens at the same time as something else:

He took off his coat as he entered the room.

Temporal as is synonymous with while (but note, as he entered would be better paraphrased as while he was entering).

as in its causal sense refers to a condition that makes something possible, or to an explanation for something.

She was able to vote, as she was now 18 years old.

They took the car to the repair shop, as it was making a noise.

Causal as is synonymous with since.