BTW, D16 intends to take a BSW and MSW. The source of the warning was an MD. 
An aside: She’ll have two courses, Psych & Human Development and Psych, done by end of high school, so the material will be somewhat familiar.
Appreciate all the feedback!
Psychology classes have a reputation for being easy and straightforward at most schools, but the MD who issued the warning might have had a different experience.
OP- If your DD is not also taking gen chem and calc, as do most freshman pre-meds, she should be fine even if psych 101 is a tough class at her school. If she takes one or the other or both, perhaps if she is still not sure whether she wants to do a STEM major, she will probably still be fine if she has at least average levels of preparation for the school she chooses to attend and the classes she takes, and especially if the fourth class on her schedule is not something too time-consuming.
It is my feeling that students who begin a major freshman year have a strong advantage as they can schedule other classes around that major, take classes in optimal sequence, and will not be stuck taking too many difficult classes at the same time towards the end of their college career. So, yes, psych101 freshman year would be a good idea for a potential psych major. Department web pages generally have flow charts to advise students.
Did she have AP psychology and do well on the AP exam in high school? If so, and the college allows her AP exam score to substitute for the introductory psychology course, she may want to skip it completely. If she wants to take more advanced psychology courses in this case, she can check her knowledge against the syllabus and old final exams of the college’s introductory psychology course.
I’m in Psych 100 at Penn State as a freshman and it’s been easy so far. FWIW, I also took IB Psychology in high school and got a 6 on the exam, but was unable to get credit because it was an SL class. Most of it is just memorization. One difference between high school and college, though, is that while the tests are multiple choice, they’re based on application of concepts rather than knowledge of the concepts of themselves. I could see how that would be tricky for some people, but it’s not too bad.
Obviously it depends on the school and the professor, but for me, Intro Psych was the perfect freshman gen ed: An interesting class that’s easy to do well in. So I would say it’s a wise choice to take it :).
@metsfanAJM I think you’ve hit the nail on the head with noting the exams are applied concepts. Thanks for this advice!