There seems to be one of the most obvious suggestions missing from this thread, although I'm sure that your daughter has taken advantage of it. The best advice she can get is from her peers about the local businesses that they have co-oped at. The career placement center at her school should have a vast library of feedback from past co-op students about the quality of their experiences.
The best co-op jobs will come from a business that takes the co-op experience seriously and offers real project work opportunities as a member of the project team. They do exist, believe it or not. Now that she has narrowed her choice to the biomed field, she should be looking for biomed businesses that are advertising co-op positions, and doing her due diligence research on them, just as if she were looking for a real full time job. She should be in a good position having prior co-op experience in the engineering field.
Best of luck to her, it's a great field to be in. Notwithstanding the negative nellies around here, engineering is a chance to be both creative and useful. I have been at it for almost 40 yrs, and never wanted to be doing anything else for a living.