I'd say she's full of crap. Snakes themselves do not have a scent. Sounds like you're cleaning up the stinky urates/feces quickly, but if you're only spot-cleaning, the tubs might be retaining some scent. You should be washing out and disinfecting the enclosures once a month. I use Windex when I spot-clean, then once a month I wash tubs in the bathtub with dish soap, and wipe down tanks with Clorox Clean-up.

Talk to your step-brother and send them to this post once you get more people confirming they don't smell unless there's poo/urates. You can use a bedding if you like, but it's likely she'll complain about the smell of the clean bedding too.