Do you weigh your guinea pig every week as part of routine care? If not, then please start to do so. Poops being smaller than normal can sometimes indicate that they are not eating enough hay. However, because poop output is 1-2 days behind food intake, it means that poop output a very unreliable method of gauging. The only way you can tell a piggy is eating enough is through the routine weekly weight checks. When you have health concerns about a piggy you then switch to doing the weight checks at the same time every day so you can more closely monitor hay intake. If you notice a piggy is losing weight or has lost more than 50g then you must step in with syringe feeding and see a vet.
In this case, the poops themselves look ok but I would still encourage you to weigh her daily for a few days to see what is happening with her weight. Then you can either see a vet if she is losing weight, or go back to weekly weight checks if things are actually ok.
On a side note, please check the diet. Banana and tomatoes should not be fed routinely. Banana is too sugary and tomato is too acidic and can lead to a lip infection called cheilitis. Any fruit including tomatoes should only ever be fed as a very small amount and as a very occasional treat.
The guides below have been added in for you to read as they contain further information to help you.
Weight Monitoring and Management
Long Term Balanced General And Special Needs Guinea Pig Diets