It's not letting me send my message?

So I recently got my friends number who has a galaxy S3 and I have a iPhone 5S. We texted each other only about 3 messages each and then all of a sudden neither of us can get our messages to go through. We can both text other people, but whenever I try to text her or she tries to text me it says the message can't go through. We've both tried deleting our numbers, making sure we didn't block each other, and my MMS messaging is turned on. It's getting quite frustrating so someone please help!

You should try removing her/him from contacts and re add then try texting again, or use Kik snap chat so on