Hi
Please take her off any fresh food and see whether her pellets normalise again within 24-48 hours. If they get worse, don't get better or if the problem recurs, please see a vet because that goes past a minor tummy upset and need medical attention.
Here is our guide for digestive problems, including mild diarrhea; you may find the practical and more detailed advice in there helpful:
Digestive Disorders: Not Eating - Diarrhea - Bloat - GI Stasis (No Gut Movement)
You can additionally help the gut microbiome to normalise by giving 'poo soup' (i.e. - when correctly done - live healthy microbiome transfer from a companion not on antibiotics) and/or adding probiotics or syringing them in a little water.
How to make 'poo soup' (which is not quite as gross as it sounds but effective if live microbiome gets into the gut to boost the unbalanced digestive bacteria in there:
Probiotics, Recovery Foods And Vitamin C: Overview With Product Links
I would also recommend to switch from the normal life-long weekly weigh-in to weighing daily on your kitchen scales (ideally first thing in the morning for best day to day comparison) in order to see whether the tummy upset is the result of not eating enough fibre or a pain issue in the body that is resulting in softer poos and is causing loss of weight. It takes about 22 hours or longer with a sluggish gut for food to pass from one end to the other, so the poo output is always running at least a day behind. Kitchen scales will give you the up to date information and are your biggest ally in managing health issues.
Weight - Monitoring and Management
All About Syringe Feeding and Medicating Guinea Pigs with Videos and Pictures
All the best!