Weight Loss Elderly guinea pig

My skinny pig, Ginny is 6, she’ll be 7 in September. I’ve had her since she was 8 weeks old. She’s the last remaining pig of the 4 I had (other 3 all passed away in 2021 of illness/old age etc.) Ginny has hyperthyroidism and arthritis, recently (October,) had surgery to remove a stone, she takes methimazole and meloxicam daily. She’s also dealt with chronic bumblefoot on and off for years. She had her vet checkup a couple of weeks ago, the only concern I brought up to the vet was she had been having on and off diarrhea for weeks that I would treat with probiotics but it wasn’t getting better the weekend before her visit. It’s since gotten better, she eats a probiotic powder on her pellets every day, she does still have occasional misshapen poops but no diarrhea. She was underweight at the appointment (590g,) but everything else is good. She has plenty of energy, eats and drinks like normal, constantly begging for treats and eats all her veggies. However her weight continues to fluctuate, as of last night she was 570g (I’ve been weighing daily since the appt.) I’ve been giving her critical care on and off, it’s been impossible to find the flavor she likes (apple & banana,) so hopefully she likes the Papaya flavor I have coming today. I’ve also been doing daily soaks & calendula cream for her feet, it’s all slowly healing.

I can’t tell if the weight issue is just her being old and maybe we’re coming to the end of her life? She has been through SO much (3 days in the hospital with bloat at 8 weeks old, hay pokes in her eyes, hyperthyroidism, stone surgery, etc,) and always bounces back quickly but this time around I can not get her to keep on weight. I sent an update with her daily weights to the vet and since everything else internally was good at her last appt he doesn’t seem to think any further testing is necessary (which I agree with considering her behavior.) So I’m just wondering if it sounds like this is just part of her coming to her end.