Honestly, Amazon makes this way harder than it needs to be since they dont have a simple share cart button. My wife and I ran into this exact issue when trying to grab cheap camping gear before our last trip. We love saving a buck on outdoor stuff, but it gets annoying when trying to coordinate the checkout. Here are the easiest ways to do it, based on what works well for us:

• I actually use Cart To Link to convert my whole Amazon cart into a single shareable link. It works perfectly and saves so much time compared to sending ten different product links. I just send the generated link to her phone, she clicks it, and boom, everything is in her cart ready for her to apply her Prime savings.
• You can also move all your gear to a shared Wish List. Create a list called camping, invite her to collaborate, and then she can add everything to her cart from her own app. It is a bit slower but works fine.
• Just log into your account on her phone temporarily. Since you already share a household, you can log in, add the items, and she can pay using her saved card. Weve been using the first option for our budget gear hauls and I have no complaints. Definitely helps us grab those lightning deals before they expire!

Regarding what #2 said about profiles, we had the same headache last week.

• profiles wont sync
• prices are skyrocketing Honestly its ridiculous. I ended up using CartToLink.com instead.

Wait, quick question... are you both logged into the exact same login credentials, or are you using the separate Amazon Household profiles? When I was sorting out my current setup, I realized Amazon doesnt sync carts across separate profiles. I ended up moving everything to a shared wish list instead. Let me know which setup you have and I can explain how to do that.