I don't think Olivia qualifies as a Brenda replacement; she was more a Lois pastiche (and silly, since Lisa auditioned for NuLois and was later paired with Ned; the character backgrounds are almost identical and Olivia knows Lois from Bensonhurst, but oh well, I like Lisa anyway). Reese I don't think had much resemblance beyond vague looks. The rest are def Brendabots.
That Kristin whatserface recurring player who was also a brunette lawyer like Claire, before? they brought in Reese, when Mo's onscreen cachet was at a particular low. Jordan was her name. Embarrassing.
ETA: Kristin Minter, that was it.