Hello bud, I'm Dr. Deb. I'll do my best to help you today.
I'm sorry for this concern for Gidget.
It's certainly possible that she experienced some sort of sting or bite while she was away from you although if this were the case, I'd expect some sort of swelling to be present. But, if suspected, Benadryl is the best drug for such a problem at a dose of 1/2 of a 25 mg tablet. Dissolving it in water is fine but you may need to use a syringe or eye
dropper to administer it to her since I wouldn't expect her to readily drink any liquid you mixed it in.
If, however, she somehow torqued or twisted her leg and now has a sprain or strain, then over the counter Aspirin would be a good choice of medication for her as long as she's not vomiting nor taking any steroids or non-steroidal anti-inflammatory drug. The dose would be one, 81 mg (low dose) tablet twice a day with food to avoid stomach
I'd also walk her on a leash when she's outside (if at all possible) so that she doesn't reinjure her leg. I'd also try and prevent her from jumping off and on furniture in the house (if she's allowed to do so).
Most dogs with mild sprains or strains will show improvement within a few days, usually 3-5 or thereabouts.
If she'll let you examine her toes and feet, then it an injury or cut may be more obvious; if that's the case, then let me know and I can provide detailed treatment options.
I hope this helps. Deb