Hello I’m sad to read your post.
I wanted to comment just to give you reassurance

I’m sorry you lost your piggy a few days ago.
I think as caring owners we do get upset, anxious and distressed.
I think losing your girl will have added to your feelings …. we always have questions what if, why etc.
I’ve read stress can come from how piggies are bred and how sensitive they are to foods etc.
My piggies are indoor piggies and I give them the best life I can.
My garden is a gravel garden and I have a dog so I’m super careful where I get grass from and what I use from my garden.
I grow dandelion plants in pots and a few herbs. I have an apple tree and a willow tree.
I’m sure your piggies have a wonderful life , you obviously care and are doing the best you can.
Try not to be too hard on yourself.
Sterile cystitis is a newly discovered health issue and great that your Vets have picked this up.
There is info on this in the guinea pig info at the top of the page.
Keep posting as sharing how you are feeling will help you to know you’re not alone in how you are feeling.
Take care as you grieve for your girl