Funny thing, if it aint broken don't fix it.. The classic lines work.. It's all about timming

So go ahead and use "long time no talk, how have you been?" after she responds ask for a drink...
HOWEVER!!!!! why are you texting... call her up, see if you can catch her on the spot

and say the long time no talk.. bla bla.. normal conversation... (say you were out of town or something, or busy in a huge project at work), tell her now you got some available time, and you would like to take her for a drink, offer 2 days,,,. i.e. "how about drink, I can teusday or sunday, i.e. a week day and a weekend day, and see what she says,...if she says she cant... ask which day she can,, and if she says wed, tell her I cant do this wed, but I can make it next wed... then you can check in with text message...
note: if she dont pick up, leave a short message "Hey, met you at bla bla, thaught you were cool, but didnt get a chance to get back to you.. Hoping I can make it up to you with dinner... Call me bacl 3-333-333-3333.... if she dont call.. then try the suttle approach of texting with somethng like this "Left you message, you must be busy also, what you up to these days" take it from there, if no reply, Next her.. Good luck
(Keep in mind, the lines that are presented in the bible WORK GREAT, but ultimatly its not the line, but the way you present yourself.. i.e. doesnt matter really what you say, but how you say it)