10 Day Old Kitten Won’t Poop

We’ve been fostering a 10 day old kitten since she was 7 days old. Since we got her she has not pooped. She’s peeing, so something must be working inside. This isn’t our first bottler, I’d say this is our 25th-ish, but I’ve never come across this problem before. I’ve heard of the triangle method, but I can’t understand what it is and the videos don’t seem to help. I am going to call the vet for an appointment first thing in the morning, but does anyone have any suggestions for now? I’ve added a drop of mineral oil to her formula. She has a good appetite and is going through about 1 bottle a day, so 3.5 tablespoons. Any help would be greatly appreciated!