NOT okay.....you need to have a talk with her and express your feelings surrounding this so she understands that what she did effects your relationship (ex: trust, respect, etc.)
I had someone sneak meat juice into my food thinking it was funny aswell as trying to switch my soy cheese with processed cheese slices. So I waited until they had left the staff room and added cat food to their meatloaf the next day and told them afterward so they could understand exactly how I felt.
Needless to say, they were mad, told me they were so sickened they 'Threw up!' and I told them that they aren't the only one. They went to my boss saying "I can't believe she did this!!!" and then my reply "Erm.....believe it, because YOU decided to put milk products in the food of someone who is lactose intolerant and meat in the food of someone who is morally, spiritually, and health-wise dead against it."
So my boss basically told them to shut up, and that after "weeks of witnessing him offend and innapropriately interact with others he finally had an opportunity to feel it for himself."
Then....a month later he quit.
That's what you get when you sneak dead animals into a v*gn's food!