Is this the total of her biology education? If she intends to use these classes to meet prerequisites for additional courses at Vandy, the summer courses will probably need to be preapproved before she takes them. The advice above to make sure you’re in the “right” type of bio class is important. Running it by the advisors at both Vandy and the proposed school to make sure is a good idea in any case.
Also summer classes are easier to bomb than regular ones as they are the same content as a semester class but at a much faster pace. Make sure she doesn’t have other commitments (job, etc) and can focus and do well in the classes, especially for premed grades. And look at the academic calendars between the colleges to make sure she will get a little downtime between terms, too.