As far as I know, "that" cannot be used after comma, whether it functions as a relative pronoun or a conjunction. However, I've read this sentence from Hans Christian Anderson's fairy tale.
So the bed of the sick girl was drawn nearer to the window, that she might see the budding plant.
Considering the context, this line has nothing to do with "so-that" clause. Rather, this is relates to "so that(=in order that)" clause. Then my question is, how come that is used after comma?