LEMORE I MEAN SEPTA LEMORE OH GOD
Heh.
The timeline might work. The Kingswood Brotherhood had been active for some years before they attacked Elia Martell’s entourage in 279, which was 21 years ago.
We don’t know much about Wenda – we know she was short, young, and fair. That might eliminate her – young might suggest that she should be in her mid-30s if she’s alive and Lemore’s definitely over 40; fair might mean fair-haired as well as pretty and Lemore has brown hair – but it might not. The stretch marks can’t rule her in or out – there isn’t any mention of Wenda becoming pregnant but there’s nothing that says she never was either.
My skepticism is that Lemore clearly has a lot of training in the Faith of the Seven – that’s why she’s on hand to train Aegon – which I don’t think Wenda would have had. Also, when it came to combat with the stone men, wouldn’t Wenda have grabbed a bow?