I'm with Forkie here, and by that, I mean largely with the model. You're trying to run a business, I get that, I'm in the same boat, but if you're serious then you know that customer service is the biggest priority. From the moment that model sat in front of your lens she was your customer, paying or not. Your priority needs to be on making those images as useful to her as possible. Referrals largely don't happen by people reading watermarks, they happen through word of mouth.
I would suggest that you apologize to her, mention that you value her time and that you appreciated the shoot, and give her the unwatermarked copies. You yourself called her wonderful, so how you would can future opportunities with her for the sake of a watermark I have no idea. The agency isn't going to hire you just because they've seen your name on a photo, they hire based on your body of work, which you have now permanently dented by removing future shoots with her.
Sure, it's a business, but what's a business without clients.
P.S: I should note that for my own personal uses, anyone (even family) who ends up in front of my camera signs a model release. A moment of paperwork is worth hours of wasted time. Simply because I have those releases though doesn't mean I start posting nudes of clients all over Facebook where they've requested them to not be posted.