if she had Louis XIV probably would have been married her off to his grandson, the Duc de Berri in 1710...
Which could have some important knock-ons...
It almost certainly butterflies Berri's 1714 death from a riding accident. So he, not Orléans, would be the Regent for his nephew Louis XV.
Berri was married to his second cousin, the eldest daughter of Orléans, and all three of their pregnancies failed. He is more likely to have healthy children with Louisa. Could fear of this be a reason for Louis XIV to bar Berri's OTL marriage? And to end the intriguing for Berri's hand by marrying him to an outsider? Also, his wife was notoriously unchaste, perhaps even before the wedding.
Say he learns of this, blows off this marriage, and then turns to the notably devout and presumably virtuous Louisa instead. This averts her death from smallpox (she would have moved out of the Stuart residence), and as suggested her brother happens to die instead.
Berri and Louisa have several children, and the Stuart claim to the British crown is now held by a French noble-royal house. Louisa isn't going to be leading any Highland uprisings; there is no 1715 rising at all. (Does this strengthen Jacobitism by avoiding losses? Or weaken it, because by not contesting the Hanover accession, the Jacobites tacitly consent to it?)
By 1745 or so, Louisa's eldest son would be ripe for a try. He might also be Duke of Berry. Could a Frenchman hold the loyalty of the Jacobites?