Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern for your dog. I assume you've already taken her temperature or plan to do so; if you're not aware, normal is between 100 and 102.5.
A fever could certainly explain her symptoms although an issue with her spine where there's mild compression of her spinal cord might also explain it since this particular problem is a common one for pure bred Dachshunds and Dachshund mixes and it can be painful.
But regardless, as long as she's not vomiting and not currently taking any steroids or non-steroidal anti-inflammatory medications, then Aspirin can be given at a dose of 1 mg per pound of body weight twice a day with food to avoid stomach upset. My only hesitation about its use would be that it might interfere with what your vet would want to prescribe if she has to be seen but a few doses should be fine.
As for her loose stool issues, I'd feed a bland diet of boiled, boneless, skinless chicken breast and 20-minute white rice, small amounts through the day. I'd also add a probiotic such as Forti Flora which may be available at local pet or grain stores.
I wouldn't advise any over the counter products such as Pepto Bismol since it contains salicylates (the active ingredient in Aspirin). There's a risk of gastric ulceration if you give her Pepto and she's also taking Aspirin.
I hope this helps. Deb