I'm going to jump in here with a "passing the buck" answer. Ask her doctor and see if there is a learning pro or con to "helping" her develop her motor/mechanical skills.
We all know of the "switch-hitter" skills that athletes develop. This actually is a form of ambidextrous and many can learn the art of throwing with both hands as well. From what little schooling I can remember, while people can develop the ambidextrous skills, they still tend to have dominating left or right functions that are hard-wired into each individual's brain.
While we all are aware of the advantages of left-handed players in fastpitch, it has drawbacks as well. Drawbacks in softball as well as other sports as it can be a limiting factor. I can only guess that a Pediatrician would advise you to let nature determine how this lil girl shapes up, I would be curious what the medical field says about early-age training and development of skills in this manner.
On a lighter note; I'd like to share a lil joke/anecdote I use with young girls when teaching them how to pitch, I think it lightens the air and makes them smile:
Young ladies are normally frustrated when trying to pitch underhand for the first time. I explain to them how this is all their parents fault. Their intervention when you were younger kept you from already knowing this skill. I explain the scenario; that at a young age as you were beginning to walk, at some moment something on the floor would catch your attention. You would waddle over and pick it up. Almost inherently a parent would say "Throw it, throw it to me" and after careful study you would toss the item underhand towards them-----beaming with joy. The parent would respond by saying "No, that's not right. do it this way" and put the item in your hand and show you the overhand motion as the preferred method of throwing. From that day forward you have practiced how to throw overhand. Now, here you are, all these years later, and they want you to hone your skills to throw underhand-------the very motion you started with as a toddler------and they told you "No". So in the future when your parents get frustrated because you are struggling to learn how to pitch, remind them it's all their fault. Had they left you alone, you'd already know how. Just saying...........