When it was my birthday she bought me a slice of cake which was nice though and gave me a little note.

Sounds like a small gift + a card/note might be a good idea then.

I would suggest something simple like a coffee card, but if you want to be mindful of caffeine intake for pregnant women then maybe an alternative like a box of caffeine-free tea that’s soothing and calming? Or perhaps aromatherapy in the same vein if she’s not allergic to scents?

Moms with small children are stressful enough on a good day let alone going through rough times, something soothing can hopefully make her day more endurable.

Plus a get well card(or something appropriate for the event) with a short hand-written note can go a long way.

You both sound like wonderful people.