It means the same as:
"She should arrive soon"
but it's a more formal way of saying it.
For example, if I was a businessman I could say:
"my client is to arrive soon",
"my client should arrive soon",
and they both mean the same thing.
It doesn't necessarily need to be about people either, so if I just ordered something online I could say:
'my amazon package is to arrive soon'
However, it usually means that the subject is already on their way to arrive at the destination, so out of the examples you posted, it is most like:
"She is not with me at my house now. But, she will arrive at my house soon"