If she’s used it anywhere already, you need to tell her. If you don’t tell her, another teenager will, and in the meanest most embarrassing way possible.
Say that while the emoji is innocent and cute, it’s from a furry porn site. If necessary, “porn is about people having sex, and furry porn is about people having sex in animal costumes” is enough.
If anyone does tease her, she can say “I just found it with some emojis, but what were you doing looking at furry porn?”