Looking at what it says about this case (which is not a whole lot) it sounds virtually superfluous whether or not anybody can find the phonied documents on her computer, if she went and submitted them to government records under her Jane Doe (which normally requires signing for them separately from the document, meaning taking responsibility for the documents’ veracity). Is there some separate crime of “having phony documents on a computer” the prosecution hopes to have her found guilty of? It would at most lend a teeny bit more weight to an already heavy case she faces.
Sounds to me, from the limited info, that it is just more evidence they seek from her computer. It is one thing to show a jury that that she signed for or signed on the document, but a lot more damning to show that she forged it on her laptop. That is why this is a 5th Amendment issue case - they want her to incriminate herself in this way by showing them that she has the forged documents.