Any degu experts that can help me? i dont know whats wrong with my degu :(?

ok so i have 2 female degus, roughly 2-3 years old. i have had these degus over a year now and while living with me they have been fed a diet of Pets at home guinea pig nuggets which i am told is the best food for them, they recieve next to no sugar, maybe just a bit of banana less than once a month. they only have treats that are suitable for degus, such as herb mixes and wheat based treats. i check my degus every night before bed and so tonight i was shocked to find the girl who is usually the bossiest and steals all the food looking very skinny. she let me scoop her out of the cage with barely any struggle at all (unusual) shes normally very curious and jumps onto ur hand but too fast to scoop up. her teeth look fine and normal to me but she has the look of a generally poorly goo and i dont know what it could be, obviously im going to book her in at the vets but any info/ suggestions would also be appreciated, i have syringed her a bit of probiotic water in hopes this will perk her up and have seen her having a munch on a bit of her herb salad but shes nott herself