I'm looking at the 1.20.11 code for this now, and AFAIK it hasn't changed.
You need at least 50,000 credits and sufficient space in the cargo bay. Tris will restock the pods up to a maximum of 5 pods each, minus what you already have in the cargo bay. So if you have say 5 or more bio pods already, Tris won't restock those, if you have 2, she will restock up to 3, etc. So the max T'ris will restock is 15 pods, IF you don't have any pods whatsoever, and less if you already have some pods in the bay already.
Also, once the cargo bay is full, T'ris won't restock any more pods. I believe that the restocking check is made at 0900, but I'd need to double check on that.
I do modify this in my gameplay mod (working on that part right now, I'm working on adding a 'choose an adjustable max restock level' routine) but I do not touch this code in my interface mod, so the original functionality should be the same.
Tris often does 'stealth restocks', with no accompanying message. I had to add a message routine in my mod to inform the player if T'ris restocked any pods.