imessage message doesn't be delivered sometimes

Hello,

I use iMessage with my wife and messages don't be delivered sometimes. It says "sent" on my iPhone 6 but my wife doesn't see the message.

We are both in Wi-Fi and 3G networks but there may be network issues instant.

I send another messages then and they are delivered. The message that doesn't be delivered doesn't be delivered still.

We use iOS 8.2

Is there any solution for this tedious problem?