I misunderstood the first time I read and thought you meant she'd shared photos of your child.
How old is your child and what does he know about your relationship? My children are all teens so would be allowed on social media and they're out and about without me, if this is your situation I'd worry that he'd simply bump into them as a couple let alone seeing photos on line.
Does he still think his parents are together? Because if he does and he sees photos or even at a later date discovers the crossover he's going to feel more betrayed and lied to.
There's a way to be open and honest with him without badmouthing each other.
I think trying to justify photos of a partner as essential to business is embarrassing but I've guessed at a couple of reasons that someone would do this. This woman has already disrespected you in the biggest way so she's unlikely to adhere to any requests to keep the relationship offline. Unless her business is howtostealahusband.co.uk?
Do your family and friends know?
At the moment it sounds like your boundaries are being set between you and your husband and you're relying on him communicating your needs and requests to the OW. I would be tempted to contact her directly and be really clear.
Also, with the divorce in mind I would definitely be keeping a record of all of this, the dates, the posts etc. So no one can gaslight you in the future for overreacting or something pathetic like that.
For your own wellbeing I would stay away from her online content. But if any of your best mates happen to stumble across her accounts you can't stop them from making comments on there or screenshotting her stuff.
Like, what is she trying to sell where it would be good for business for people to know she's broken up a marriage (yes, I know this is also the ex-husband's fault)? I'd have thought that would be terrible for anyone's brand.