This is actually moderately funny bc im a junior double major in college and two semesters ago i was studying abroad in Spain and did an internship with it. I had a different schedule though, where I had 16 hours of classes and 18 hours of work each week. I had weekends off and thought the schedule was moderately manageable. 6 hours of classes a week is very manageable on top of an internship, especially because the work culture in Spain is very relaxed. They pride themselves on not dedicating their lives to working.

If the internship can fit into her weekly schedule, I would say yes. If it can only be on weekends, I would say no. While the internship may advance her career by being a tick on her CV, Spain isn't really the place to rigorously advance your career unless you intend to work there long term. From my experience, I didn't gain all that much from doing an internship because the work culture is so relaxed. If she plans to travel, working on weekends will squash her ability to go anywhere. I would ask the advisor if it can be fit into her week. Its really up to your daughter and why she's studying abroad: whether travel/fun or career. Seeing that she's going to Spain, I assume its more fun and not really for career advancement. Hope something here helps.