To me whether or not she should is not necessarily the point... I mean, yes if she wants them, understands the commitment etc. Sure.
But more importantly to me is giving her several options. You mentioned her hair gets tangled super easy and that she doesn't like brushing it... So if you're looking for alternatives to the current hairy situation

Are there other options for her other than dreads? Like getting it cut short or braided or ?? Having several options would give her the freedom with this decision.
And I think hair can totally make a social statement, or at the very least a fashion statement. If she's ready to make that commitment, then why not go for it... Depending on her personality she might really enjoy having them.