Hello, as a licensed veterinarian I am happy to assist you!
Backward or "reverse" sneezing can be a common behavior
in breeds like the Shih Tzu and can be quite disconcerting when it happens. The good news is that it is typically not a problem, requires no treatment, and will go away on its own.
However, some dogs can become a bit distressed by it and it can persist for some time in some dogs, as you've seen with Daisy, so there are some things you can try to help alleviate this.Reverse sneezing
occurs when the tissues in the throat spasm- often due to excitement, exercise, or irritation/stimulation of the throat. Therefore, to help stop the reverse sneezing, calming the dog down is the first step; try soothing talk and stopping her play
/running around. Then, you can gently massage the throat- gently squeezing her throat with your hand. If this is not enough, you can also gently pinch her nostrils closed- this will force her to breathe through her mouth which helps decrease the spasms.
I do want to note however that if this is a new problem for Daisy, a vet check-up may be worthwhile to make sure there is not something in her throat (when small items get lodged in the throat it can cause reverse sneezing that doesn't go away as easily, for example). I also recommend confirming this is definitely reverse sneezing, as sometimes coughing can look similar. Here is a video of a dog reverse sneezing for reference:
I hope you find this information helpful. Please feel free to contact me with additional questions and please remember to rate my answer when you are satisfied so I receive credit for my time.