How can differentiate between iPad and iPhone iMessages for same contact

I have my sister in law's email and phone number all in the same contact. She iMessages me from both her iPad and her phone. They come up as two different iMessage conversations, but they both are under her name. When I go to text her I don't know if I'm sending it to her iPhone or iPad. Anyone know if there's anyway to differentiate? Sometimes looking at what was previously said in the conversation helps but I can't always remember (nor do I know which device he was messaging me from in the previous convo). Thanks all