I think Erika might become Lisa's achilles heel if she's not careful.

Erika is quickly becoming a favorite, and this would be fine if it weren't for the fact that she can't be manipulated.

She is strong minded and level headed enough to not sweat the petty stuff, such as Dorit's panty accusations.
She keeps an arms distance from all the girls, never allowing them to get close enough to see the cracks, so Lisa can't even poke at them. Lisa tried to get a rise out of her at the Gatsby party and failed. In fact keeping a healthy distance from the rest of the ladies is a tactic that Lisa has employed since season 1, so it's interesting for Lisa to encounter a women with a similar demeanor.

Erika doesn't seem particularly interested in striking a friendship with Queen Bee Lisa either. Which is something all the other housewives seem to want to do when they're not backstabbing her.

Erika also has her own brand and her own enterprise, albeit not in restaurants like Lisa, but in music.
She is quickly becoming a gay favorite, and with 2 of Lisas restaurants in the heart of West Hollywood (boystown) she definitely understands the value of the pink dollar.

Also, did you guys notice how many compliments Erika was giving about Kyle's character in the episode where they went to Greece? And now all of a sudden Lisa is so vehemently defending her "friend" Kyle?
I don't think this is a coincidence. I think of all the ladies in RHOBH, Kyle has always been the most loyal and substantial ally to Lisa, and Lisa didn't always appreciate it.
Now that Lisa see's Erika sweeping Kyle of her feet and taking her to Greece for fun, Lisa might be threatened about that too.

I see Lisa and Erika as 2 magnets. Both powerful but repelling each other on contact.