['I am blushing so bad right now, sometimes technology is not my friend.', 'I can relate.  Sometimes I have issues with new tech.  What is giving you problems?', 'I was texting and flirting with this girl and then a female coworker messaged me about work, and not seeing who i was responding to, I typed a message that was not meant for her.']
Ouch.  That is awkward.  I imagine you can just explain to her that the message was sent to her by mistake.  It happens.
I was texting someone and then I accidentally sent a message to the wrong person.  It was pretty embarrassing