Holistic vets may have some options but to go against accepted medical practice that has valid research data is where I draw the line.
I seriously doubt the heartworm meds have anything to do with her gi issues. People who tend to go holistic always believe they are poisoning their dogs with preventives. It is an ongoing problem for our pups imo.
And, as I said, you can get Ivermectin...it has nothing added to it.
When you have time, I strongly suggest you peruse this website. Heartworms are no joke. I am always horrified when I hear horrible advice on this topic. I have had dogs probably longer than many here have been alive and none have ever suffered as a result of heartworm prevention. I have, on the other hand, seen yorkies die from heart issues due to damage from heartworms and/or heartworm treatment. There is actually a post on here about a pup that came to our rescue and died...broke my heart when it could have been prevented if her owner had only given her that one little thing per month.
https://www.heartwormsociety.org/