Okay, first off, I want to mention right off the bat that this is giving me some major Harry Potter feels! I’m just saying, that you could easily mistake those horses for Thesterals.
Now on to the meat of this passage! I really want Clare for once to be freaking consistent about how integrated into modern day society the Shadowworld really is. I mean in the last two chapters we have seen them use a refrigerator, a microwave, and a telephone. Yet, the Brother Jeremiah is rolling up in a freaking horse and carriage in New York City? Yeah no, that doesn’t work. Clare has to choose one or the other, and she has to give a damn good reason why the Shadowworld is not intergrated with modern society and techonongly.
I am once again going to use Harry Potter for an example. The reason why the Wizarding World is not really integrated with modern society was because 1) magic has really adverse effects on modern technology 2) The reason why Wizards separated the Wizarding World from regular humanity in the first place was due to Muggles persecuting them. Yet, Clare has yet to firmly tell us how much the Shadowworld is integrated with Mundane society, and what technology level the Shadowworld is even on, and why! This is a massive plot hole and a worldbuilding failure on Cassandra Clare part. And at this point, I just want to throw a stack of my writing books at her head.