Why cant she just stay communicating? ?

So me and my girlfriend have been together for a year now. And during this time it seems like she doesn't make an effore to communicate with me as I do with me. When we r not together I always try to txt her no matter how busy I am. However when she goes out or is out with friends or just out and about she doesn't seem to take time to send a simple txt to see how I'm doing or to respond to my txt. When I ask her why she's not responding shell have some excuse of being busy with something. But how busy can someone really be to not be able to send a text msg? Pls help what to do...