iPhone hacked?

Hi - I texted my friend with a couple of emojis from my iPhone 5 (8.3 OS) She received an extra emoji - of a skull in a box, that I did not send and is not even one of the emoji's on the phone. This was the second skull like that she had received - the first from someone else, so the problem may be with her phone, not mine. On her advice, I deleted my emoji keyboard, but have otherwise not noticed anything unusual with my phone. Has anyone heard of this? No one else has mentioned receiving skulls from me. Is there a way to check as to whetherThanks!