Wendy's hatred isn't odd, it's quite common, especially here in America. Rank and file British citizens (Republican and Monarchist alike) and talk show hosts over there don't really have a problem with Meghan and they love her mother, Doria. LOVE HER.
Here in the States, their problem with Meghan in America is that she got above her raising by marrying Prince Harry. Half-breeds (especially mixed with black blood) aren't supposed ascend into The Firm with a big, grand spectacle out a Disney movie and have access to Princess Di and The Queen's jewelry. Why? Because they're not. "Why should she have what I'm not going to ever get? It's not fair."
That's why they accuse of her being an opportunist. Nevermind her and Harry are a love match that connected through a mutual friend, oh no, Meghan was plotting to get into the Royal Family and did so! The horror!
Her family is no different; they don't give a fuck about her, they only care that she married into the British Royal Family and they think they're entitled to perks and money and Meghan is in the way of that.