Maybe I'm unforgiving but if I am treated rudely in a store I usually don't go back. If that were me, I probably would have pointed out that I was just about to spend over $50 but maybe I should shop online instead, where I won't get any attitude.
I can understand why they'd be concerned, but they way they approached it would, for ME at least, have the exact opposite effect of what they were trying to accomplish. In my opinion, brick & mortar stores need to focus on SERVICE, since they aren't going to win if you're only considering price. There needs to be a reason for me to come into the shop, and rude storekeepers, regardless of their reasoning or their assumptions, is a huge turn-off.
If she'd come up politely and asked if she could offer assistance, and maybe said something like, "I noticed you taking a picture, we discourage that because blah blah blah" and been PLEASANT about it I wouldn't mind at all. Especially if they have a sign posted somewhere that I'd missed.
I do see signs now and then, in LQS's that say "Please no pictures". That doesn't bother me a bit, and if I missed the sign or had a brain fart and whipped out my camera I wouldn't feel annoyed if a storekeeper reminded me in a reasonably polite sort of way. But no signs and a huffy employee making assumptions about my motives would be a pretty clear sign for me that this isn't a shop that suits me.