I have a contact with two phone numbers. How can I figure out which number is associated with a specific text?

[ItsAShaunParty]

This problem happens to me on occasion. It's very frustrating.

For example, today...

1. My friend got a new phone number.
2. I added it to her contact.
3. We texted. (She has an android, so texts are green.)
4. Later, I texted her and it went to her old number.
5. They were pretty mean about it. At least they had iMessage (blue texts).

So, I have two phone numbers under her name in my contacts. How can I figure out which number is associated with a specific text message? Is there an easy way?

Thanks!