Switching between iMessage and text without needing to turn off wifi/data

I have an iPhone 5 with a data plan and my girlfriend has an iPhone and iPad both without data. Often she leaves the house with her iphone but leaves her iPad at home connected to the wifi. Whenever I want to send her a message it sends as imessage and goes to the iPad that is sitting at home and doesn't make it to her phone. To get around this I need to turn off data and wifi so my phone only has cell signal so it will send the messages as a text rather than an iMessage. Is there a faster way to do this so I don't need to keep switching data and wifi on and off? I've tried holding the message as its sending and click send as text message but that hardly works.