OK, Diowe, I think this is all very, very good thus far - especially given that she'd already read the first 50.
What I do know about Anderson Literary is that Ms. Anderson was once a part of Anderson/Grinburg. The partners split & began their own agencies. This would indicate to me (again, gut feeling & not fact), that both outfits might have a higher than average rate of requesting more material, which in turn might mean they have more on their plate, which ultimately might adversely alter the 10-12 weeks they'd said was their timeline. This is not an indictment against them at all -- but it does mean that patience is important here. This I say from recent experience wherein I was actually applauded by an agent who apologized for a correspondence delay, then was impressed by how I replied in a no-worries-I'm-patient-and-understand-your-clients-come-first-which-is-why-I-love-you-greatly kinda way.
This is all excellent so far, Diowe. Try to stay cool & patient. And though it may be torture, I would say that since you submitted end of June, well... October 1st would make a fine date to drop her a line if she hasn't yet gotten back to you.