First, I would make certain that that instruction is not listed in the places you mentioned. Don’t rely on your memory, but try to look at the actual documents again.
If you see no evidence the specification was made, I would calmly ask her where it is listed because you don’t remember hearing the instruction and you don’t see it in the two places you mentioned in the first post here. Either she should be able to tell you how your class was informed and you will have to accept her judgement, or she will realize she didn’t make the specification clear and she will modify your grade.
Caveat: If she says she verbally spoke on this in class and it’s possible you missed one or several classes, that might be a complicating factor.
Caveat 2: If nearly every other student did the assignment the correct way, it undermines your position that the instructor did not make that specification.
The last thing I’ll say is if you come to realize she actually made the specification and you forgot about it, then you should simply admit that to her. Ask for a second chance, accept a deduction if she deems it necessary, ask for extra credit work, all that. But if you realize you made a mistake, don’t try to make it seem like it was her fault. That probably won’t go over well.