I know I have to take the pet to Merana. But where and when? Thanks!

When she's on the map (random) Complete the quest with the pet you want changed active

Thanks...

[edit] Does she show up daily? I have checked nearly every hour, except when I was sleeping, and she is 'nowhere to be found'. :'( Google isn't much help... there was an instance where it says she was accessible for 12 hours. Is that the case every time?