Hi @jptech and welcome to the Forum 
I think this is happening because Jane is replying directly to your email in which x+12345@mail.asana.com is still CCed > this explains why a new task is created.
In order to create a comment from her inbox, Jane should enable her email notification and reply to the notification she receives from Asana to let her know you added her as a CC > By replying to this notification, she will create a comment on the task
I’ve added an example of the notification email I’m referring to just below (note that the notification comes from “reply-d43793hifgirgfi@asana.com”, which is an email address you can reply to!). You can also have a look at this handy article from our Guide to learn how you can reply to notification and create content in Asana
