Positive reinforcement is where a child wants/needs something, behaves in a certain way that they know will get them the thing, and are then given the thing. I feel it's necessary but it must be used correctly in order to benefit the child. So for example, when Abbie wants candy, she asks for it, and it's almost always given to her. Or she wants attention, throws a tantrum, and is given attention.
What they should be doing, first and foremost, is paying attention to her cues to anticipate her needs. So instead of responding to a tantrum with candy, try to discover what's setting her off, find a distraction (sensory toy, etc.), and so on. This automatically respects the kiddo more than just punishment or a blanket "reward" - you're actively trying to understand where they're coming from.
Now a beneficial example of positive reinforcement might be my daughter wanting a new toy, us agreeing if she earns x number of stars on her chore chart, and then getting her the toy and giving her praise for completing her tasks. This isn't us automatically giving in or turning her down - it's just reinforcing that when you want new things you have to work a bit. Now you could set this up as a regular thing if you're able or just allow it once and a while - either way make sure you're still giving praise.
Again, keep in mind my daughter has a much older adjusted age than Abbie. I would definitely need to heavy duty brainstorm to come up with a workable plan for her. But I do think it's doable, just not for the lazy ass Maass family.