I always thought it was a little silly when people say they want to take Latin because they want to go into medicine. I don’t really see how beneficial it could really be, especially when you consider what you would have to sacrifice to take it. I think there’s a belief that Latin will help learn the terminology in medicine, but to be honest, you really don’t need to take any Latin (especially not years of Latin) to learn that terminology. Students do it quickly all the time, and once you pick up the roots, you can parse out what tons of new terms mean. Many of the roots students will already know from exposure, and they can pick up the few they don’t as they need them. If you really wanted to, you could probably learn all the roots you would need in medicine in an afternoon. You don’t need to take Latin to do that, and you certainly don’t need to be taking years of Latin to help with medical school. The benefits just aren’t that great to make it worth it, in my opinion, and while some students may consider it helpful, it certainly won’t give you any benefit over another classmate who didn’t take Latin.
Spanish, on the other, can be a huge benefit to a physician, especially if you get it to the level where you could practice in Spanish. If she thinks she might want to work in an area with a large Spanish-speaking population, then it will likely be beneficial in a wide variety of areas, including potentially medical school admissions, patient care opportunities, and job placement. I’m not in medical school, but I went to graduate school in a healthcare field and work in a hospital. Foreign language skills (especially in a high-demand language like Spanish or East Asian languages) always gave applicants a boost in admissions to the program and in hiring health care professionals (including physicians) in our division. No one would have cared if they took Latin.
That being said, she should take the language that she’s interested in. If she thinks Latin is really cool, then she should take Latin. But if she wants to take the language that is most likely to be beneficial to her (as a future doctor or as anyone really), then she should take Spanish, hands down (or whatever foreign language is most common in the area that she might like to live/work in or perhaps even the language of a place she would really like to study abroad in).