I had a black more about 15 years ago that got a piece of gravel stuck in it's mouth fora few hours. I wasn't sure what to do. I eventually called my friend over and put the fish in a small bowl with some fish water. I planned on taking a needle or something (can't recall exactly) to try to push the gravel out of the mouth. Just as I was about to, the gravel came out and I was relieved.
theres not much to do other than pray I hope she does ok!!
a betta pellet seems to be way to small though...are you sure thats what shes chocking on? if your guppy cant swallow it, surely your betta cant