What would make sense to me is making two posts with the different orientations seperately if there’s photos you like from both.
this absolutely does not make any sense. if you use the platform for marketing you want to group the pictures by their content, not how they best suit the feelings of the photographer.
how do you push two different posts of the same thing? you lose reach and interaction, it doesn't make sense.
you need to learn that you're doing product photography here, not art. it's your job to make it work for your client, not the other way around. she's trying to sell her brand, not your photography.
what you should do is provide vertical shots only for her instagram. crop them to 4:5 for regular feed-posts and to 9:16 for stories and reels. that way you still have creative control and she can post them as she needs.
landscape is not suitable for instagram, especially when you're trying to sell something.
the one that's already my go-to lens most of the time - the Sigma 18-300mm f3,5-6,3.
not the fastest, not the sharpest, i know, but i love it.