Due to your dog's age and the symptoms you describe, it's possible that she does have a heart or respiratory problem, and this can only be definitely diagnosed by the vet, after a hands-on exam and possibly, some testing. Pansies are thankfully, non-toxic to dogs, but many other flowers and plants are, so if she has gotten into your mom's flowers, and she's eating grass, she may feel nauseous, and dogs will eat grass to try to throw up.
Clonazepam can be given to dogs for seizures or anxiety, but only under the supervision of a veterinarian. In some dogs, instead of calming, this medication can have the opposite effect, and cause hyperactivity and aggression. You can read more about the dosage and side effects of this medication, here:
Other anti-anxiety medications, like Xanax and Valium are sometimes prescribed for dogs with stress and phobias, like during thunderstorms, when strange people visit, etc. The most appropriate medication for your dog's anxiety and other conditions must be prescribed by her vet, after an examination.
Excessive panting may be caused by various factors, and you can read more about this, here:
I hope you're able to have your dog evaluated by her vet, as soon as possible, and all will be well, once she's diagnosed and treated.