If she was under 18 on 31 December 2014 you can still ( at least for the 2014 tax year) claim her on your return as a child dependant. Regardless of whether she files or not.
Also you do not need a new on-line account to create a return for her. Go Tools, then Return Manager, then Create a New Return.
In fact it would be valuable to let her step through EasyStep to create a return, just to learn how. Note that if she is a first time filer, she will have to file by mail,submitting a copy of her T4. Better yet, she could fill out a real paper return from the Post Office and learn some valuable tax insights.
Filing is always a good idea because you establish a master file at CRA, generate RRSP deduction room for the future, and may possibly pick up some credits along the way.
