“Hey Bethany Mandel. Anybody can create, edit, comment on, etc. a Wikipedia page. Certainly a page about a person can be edited by that person.”
I agree that she could take constructive steps, but it’s not quite that simple. Wikipedia does have conflict-of-interest rules. You aren’t allowed to edit your own biographical article. (Of course, people have been caught doing so, and I assume some have gotten away with it.)
What Mandel could do is to edit the talk page associated with her article. She could sign a post to the talk page in which she noted specific problems with her article (things that should be changed, removed, or added). Then editors could consider her objections.
For example, she complains that her article is a collection of her “worst moments”. If something unflattering about her is false, she could say that. If the article is biased because it presents only one side, she could suggest favorable information that should be added. (FWIW, some accolades that she’s received are in the article — not buried, but in the second sentence. She could point out any others that have been omitted.)
If she put in the work to do this, what would Wikipedia’s editors make of it? It would be interesting to see how they responded. My guess is that she’s already moved on, though.
Nevertheless, as you point out, there are mechanisms for correcting both factual errors (including vandalism) and bias (such as Mandel claims) in one's bio page. The Talk page would be good for that.
In addition, she surely knows people who are sufficiently unrelated (not family) who could make corrections and additions on her behalf, as long as the changes meet the guidelines for citations, NPOV, etc.