IPhone texting Galaxy S3 problems?

I've recently begun talking to someone who has a Galaxy S3 and I have an iPhone 4S. Whenever I'm texting her, sometimes she doesn't get my messages, even though it's been sent from my phone and doesn't show that it was messed up. What can I do to fix it so that she get's my messages?

Chances are she previously had an iphone, so your messages are going through iMessage. You'll need to change her settings in your phone from iphone to mobile phone, and she will need to log into her old phone (if she has it) and turn OFF all imessage.

There are other options but that's the easiest.

Nope that's not it. I'm the Samsung user and never had an Iphone. Plus we used to be able to text but now cant and neither of us upgraded.