In 629 Jakob says "we both renounced love for our birthright"
So I'm assuming that Erin rejected Cherry in the past to concentrate on training her skills and abilities - where a love interest would be a distraction.
I'd agree that Jakob was most likely referring to something like that. And Cherry's interest in the wiccan stuff may have been all about getting close to Erin. But 621 gives us a bad impression of Erin's attitude to Cherry.
Erin and Aiken were apparently having sex at Christmas 2006 (256), which by my reckoning was Erin's last before coming to Wilmot. No doubt Aiken described this as channelling his energies into her. And there is some correspondence between Erin's sexual "energy" and her magical abilities. Perhaps this really was a loveless exchange of fluids. That's what Christmas is all about, I suppose.
But Cherry knew both Erin and Aiken. She knew that Aiken was mentoring Erin (272). And she knew about - and was involved in - the wiccan stuff. Yet when Cherry asks Erin in 621 "Do you love anyone? Ever?", Erin responds with a simple and apparently quite sharp "No." Surely Cherry could have been made to understand Erin's situation with a little more kindness?
But perhaps this is simply chronology. Perhaps 621 marks the start of a conversation that leads Cherry into wicca's world.
As it is, 621 suggests something more than a simple laying off. I don't think most people see loving someone (anyone) as being a matter of choice. Erin's answer may simply be a lie - an extreme form of "It's not you, it's me." But she implies that she's saying it so as
not to be lying to Cherry.
There's a big difference between keeping your emotional distance and not loving anyone - especially if you
are still having sex with people. We don't know how selective Erin was in her choice of sexual partners. But
partners doesn't seem quite to be the word, and it doesn't look like she showed due care when selecting Cherry.
But...
That skype call (489) where Erin masturbates to get Aiken up to "five bars"... that just seems somewhere between sad and weird. It would be nice to think there was some mind control going on in that relationship. And that might make Erin's earlier attitude to love something akin to Miriam's closed legs policy. And it may let her off the hook regarding Cherry.