I'm a hygienist since 1999. I have a bachelors because I went back after my associates. However, the school I went to no longer offers assoc. degrees. With a BS you can become a rep for a company, teach clinical at a hygiene school, run a community dental health program. With a masters you can become a professor in dental hygiene programs, conduct research and surely many other things I'm not thinking of.
Dental hygiene is a fun career that allows you to meet many people and serve the public. In my opinion, the best hygienists are "type A" personalities who are a bit obsessive compulsive. You have to be able to go with the flow, too, because you never know what a day will bring you. Being self driven is also important.
There are cons of being in any profession. Some for hygiene include often lack of insurance and benefits; back, neck, hand, and wrist pain; high stress levels.
Pros include flexible schedules, good pay, free dentistry.
I'm sure others could add to the pro/con lists.
If it were my child, I'd encourage her to look towards a bachelors degree because there is a high rate of burnout. You want her to have other options if she decides patient care isn't all she wants to do. It is possible to work and make money and go back to school, but it's so hard. I was already a mom and had to go back to school at night and work during the day. I was only able to do it because I had help from my family.
I also agree that she should shadow in an office.
I wish her good luck in her chosen profession!