What is going on may be entirely ethical, though questions remain. Multiple papers based on a single model is fine, even typical. Such papers can legitimately be written by different authors. Still not a problem.
But the originator of the model needs to be credited with its creation in any papers that result. Citations need to be given when possible. Otherwise it is plagiarism.
I don't think you need to be a co-author on the other student's work but you need credit for your work in anything that results.
And, you also need assurance that you won't be plagiarized and you need to deal with that issue soon, since the other student is not experienced, I expect.
Even giving editable documents to the other student may not be as big a deal as you think, since information can be extracted from pdfs as well.
Talk to your advisor and make sure that appropriate assurances are in place. If the other student is publishing a variation or an expansion of your work it can be completely valid. Perhaps a meeting of the three of you can provide assurance here. If everything is ethical, then no one should object to such a meeting.
You need to assure yourself that no one is "stepping on" your current work or plagiarizing it. But, in general, creating a model is not a "hands off" signal to everyone else.
The question of co-authorship may still be open if parts of your work need to be included in the work of another. But that might also require some additional work on your part to complete the work of the other student. That can be part of any conversation.
