Call in the middle of the night, that same night and make sure you are drunk. If she answers say something and sounds like you woke her up say "oh did I wake you? this isn't a good time? my fault I thought you worked nights for some reason. call me tomorrow when you're free then." If she is up and ready to talk, just go with the flow. If she brings up why you're calling so late, act like she's weird for questioning it and say you always do this and no one else thinks its weird. This keeps her on her toes. Talk for about 15 minutes and then say you have to go do something.
If she doesnt answer, don't leave a voicemail as soon as it beeps. Wait for about 20-30 seconds while banging things around and coughing. Then go, "hello?...hello? Oh, its ____, I was just calling to see what's up. Call me back when you get the chance." When she calls back, refer to what was said about her picking up in the first place. If she tries to question anything you've said or done, again, make it out like this is normal for you and she is the only one to ever say anything. Make her feel awkward for pressing the subject. If you doesn't mention any of that though, just go with the flow. Again, talk for 15 minutes and then you have to go to the gym/cash a check/drive your grandmother somewhere. From that point on keep things as texts but be normal, sober, and personable.