Definitely do not give her asprin. Dogs cannot digest it and it can cause liver/kidney failure and damage. I do not know of anything you can give a dog to make a heat more comfortable. If she is this uncomfortable, I strongly recommend spaying her after her heat. :)
He's your friend,your partner,your defender,your dog.You're his life,his love,his leader. He will be faithful and true to the last beat of his heart.You owe it to him to be worthy of such devotion
Dogs can take asprin, it is tylanol and alive that are deadly. Asprin can cause stomach ulcers.
Dogs in season are meserable becuase they want to be bred. A dogs season is not like a womans period. She is not experencing cramps, or bloating, or PMS or anything else. Her mysery is her raging harmones and mindless state of being as her body takes over.
She dosen't need drugs.
On the best of days a dog is a dog, and on the worst of days a dog is a dog.
I wouldn't give her anything. She really doesn't need it. I take it you plan on breeding her in the future? If not I would get her spayed. Here is a great site to explain all you need to know on heat, breeding and welping Shih Tzu. I have used the information for years in breeding my own Shih Tzu. http://www.debbiejensen.com/ Good luck