if like me this achievement is treating you badly (tera's line busy, or she's doesn't do group scenes anymore etc etc) the following worked for me
1. return to start and reload game
2. load a save that is not the auto save, (when i tried with an auto it didn't pop)
3. start a multiple person activity (snatch worked for me) these activities have extra circles near your character
4. call tera on the phone
thanks Willkat98 for the headsup
edited for spelling