It is strange that the fever isn't responsive to Tylenol or ibuprofen. That makes me think that she might have a bacterial infection. Is she acting like more than a cold is going on? I actually don't usually take temperatures or treat them unless my child is clearly miserable. My DD is a high fever kid and can go up to 104. My DS1 starts to vomit around 102 so that is a high fever for him.
I personally would not be worried at all with a fever of 99.9 unless it is ongoing (weeks or at the end of another illness).