I have no firsthand knowledge, BUT:

On Pinterest I recently came across a picture of Marianne that said her mother was going to chop all of that hair off in her daughter´s sleep, because she finds it so annoying, inappropriate, whatever......

Now that is complete nonsense.

For one thing, Marianne has been a grown-up person for years and years and does not have to listen to her parents anymore at all. (She should be almost 40 now.)

Second, in a German TV feature about her that was broadcast years ago, it was said that her parents have always supported her in her quest for long hair, and that they appeared to be proud of her and her hair, too.

Given that utter nonsense posted on Pinterest, I would conclude that the picture you saw is a fake - unless Marianne herself proves otherwise.