iMessage "delivered" but not received

Hello all,

Me and my fiance both have iphones 4. both runing IOS 5. with different Apple ID's

both have Imessage on and with the viewing read option on (the one that shows, when u read the message).

here's my issue; when i send her a Imessage on my iPhone it says "delivered" however she never gets them, so i always find my self having to click the message again and having to send it as a regular text which is becoming really annoying since me and her text ALOT!!. but the issue is only happening with her, with all my other friends using iphone4, 4s, 3gs, and ipod touchs running IOS 5 it works fine.

Any ideas on what i should do. thanks to all.