Dogs typically eat grass and other plants when they have upset stomach. If this is sudden then the dog may be having upset stomach from a bug or something more long term like IBS (Irritable Bowel Syndrome). If the dog has always eaten grass then it likely started out as a cause to settle the stomach and later became a habit.
The bad news is grass is not healthy for your dog. It will cause vomiting and thus cause more irritation to the stomach over time. It can also cause a blockage. I am very concerned about him eating Lantana Plants. These are toxic to your dog and can cause a host of symptoms including Vomiting, diarrhea, labored breathing, weakness. Liver failure is also common after prolonged exposure.
You have to keep him from eating this as it can make him quite ill.
If she becomes lethargic or you notice blood in the stool or vomit, she needs to see her vet promptly. I would recommend skipping her next meal and allow her stomach time to rest first. Often the GI track is in such a uproar that anything put in it will come back up. Make sure it is a couple of hours before her next meal. I would then start her on a bland diet of boiled chicken and rice to help settle her stomach.(1 part skinless chicken Breast to 3 parts white rice)
I am concerned with her becoming dehydrated as this is quite serious with dogs. I recommend giving her unflavored pedilayte to replace the electrolytes.