I've seen it alot lately where everyones asking why didn't she reply after 20-30minutes, or maybe an hour or 2.
The simple answer is she is busy and has other things to do (not necessarily better things) and you shouldn't let this eat you up or worry excessively.
Step back, relax and you'll get a response within the 8-24hours you sent the text if you haven't screwed up.
If not, probably rethink what you sent (:
##also the main reason for a text is to get to it when you have time -- same applies to facebook messaging