Alright, now I'll try to argue against it, or at least pose potential hurdles to overcome.
First off, why would Murphy name her children Maeve and Sarissa knowing their fate. Or, did she already name them that, so in one reality/alternate reality it's set in stone.
Second, does Maeve or Sarissa look similar to Murphy? Surely genetics would play a part even if the mantle had shaped Murphy into Mab's appearance. Or do Maeve and Sarissa simply look like Mab, so the genetics actually get changed to Mab genetics.
Third, WOJ has it that Mab and Titania are actual twin sisters. (I can propose a set of conditions that fulfill the requirements here but it requires two Murphy's from two alternate realities and Harry's joke to Murphy about a evil twin)
Fourth, It's likely someone would know Mab's identity in Faerie, particularly Lea, who rose to power with her. So, throughout the series, Lea would be fully aware of Murphy's fate. And most certainly would Vadderung, and the other highest powers. I'd argue that Nic/Anduriel does too because Mab, supposedly our Mab, had to make a great many deals (one with Nic) in her takeover of the defense at the Outergates. It would put a new spin on things with Nic/Murphy and Nic/Mab faceoff during SkinGame. Mac also has history with Mab, so its possible when Mac was IN, he was in a position to know. (See SG and greetings. See Murphy face off against Tiny in Small Favor: Mac is impressed and gives them REAL mead.) I'd estimate that the Gatekeeper knows, he has been their the longest, and is the eldest of the wizards. )
Fifth, Any time plots worth their salt would try to aim at undercutting Murphy's ascension to Mab. Though, if true, it would be fairly difficult to disestablish that once it had occurred 1000+ years ago.
Sixth, Murphy would need to time travel back 1000+ years ago, most likely with Harry. They would have to participate in events and overturn historical inertia. Murphy would need to supplant a Winter Lady. She would need some time and team up with Lea. She would then given an event that would take out both Winter and Summer Queens ascend to Mab. This event would coincide with the last time things got off/awful in the wizarding world. Given this, a book would probably need to revisit around the Battle of Hastings, perhaps around the time where Merlin created Demonreach at one of the points in time. Team Good launches counter to Team Bad at this point in time which gives Team Good license to time travel to then and affect change.