M.P.
I agree with Annie A. Both my daughter and my granddaughter, as a toddler, vomited easily. It's a physiological and a psychological thing that they cannot control. We have to work around it.
I first suggest that you accept that it happens and pay as little attention to it as possible. It certainly does help that she runs to the bathroom.
Then, I found it helps to have a somewhat of a ho hum attitude about the medicine. Again making it no big deal. Pharmacies will flavor medicine but my daughter could still taste the medicine. I would give her a choice, which sounds like what you're doing. The choices I allowed were to put it in juice or not; take it now or 15 minutes from now; use a spoon held by me or a medicine tube held by her. We talked briefly about being a big girl and how this medicine helps her be healthy. But I found that any long discussion did not help. I adopted a this medicine is absolutely necessary and there will be no discussion other than what is necessary to make the choices.
If she didn't take the medicine, there was not TV, no toys, no desert, nothing until the medicine was swallowed. The whole exchange was calm and matter of fact. I had to work on developing this attitude and didn't actually have consistent success until I used it with my granddaughter. My mind tended to say, "this medicine is important and must be taken right now! which then led to a slowly building panic when it didn't happen. At first, I had to take a break when I realized my mind was working overtime or my feelings were rising. Now I can just stand or sit there and say it's now or the TV goes off, the book/toy goes away, or there will be no dessert/snack until this is done. I tried to inject humor. Sometimes I was able to and that also helped.
I forgot to add the suggestion that it might be easier for her to take a pill instead of liquid medicine. It was around this age that my granddaughter started taking pills. She made the request which surprised the doctor. She had no difficulty swallowing pills.