Hi Livvje1010 -
We do use glycerin suppositories in animals occasionally, but many times when an animal is constipated this are just enough enough to do the job. It is often necessary to give repeated enemas and to "dig out" the poop using a gloved finger. This is something that requires sedation in most cats. The suppositories are usually only effective with very mild constipation. So, the answer to your question is yes you can use it, but it may or may not work.
Do NOT under any circumstances use a an over the counter enema on this kitty. This will cause severe changes in the blood electrolytes and often are fatal in cats.
You should also be aware that many owners will mistake straining due to diarrhea for constipation. If you think your cat is constipated simply because she is straining, then I would recommend having her checked by a vet to find out whether she is straining from diarrhea or constipation before administering her anything. If you have already been to the vet and they diagnosed constipation, then you can try the suppository.
I hope this information is helpful. If so, please click Accept. If you have additional questions, please let me know.