Coming from under my slab is a 1 1/2" pipe that is threaded on the top. I am trying to connect an elbow to the pipe run another piece of pipe then another elbow up into the new shower drain. I went to my local plumbing store and they do not have threaded elbows so they told me to just glue the two pieces together same as I will do for the rest of the pipe. Does that sound right? Or is there a better way to connect the two? Thanks for your help in advance!

Is that your old shower drain ?

It should be OK to glue 1 1/2" fit-in female adapter and 1 1/2" 90. However, I would not attempt to screw it on galv. Pipe. I would rather use 1 1/2" Ho-Hub coupling with 1 1/2" Street 90. It is much better connection.