Combining experience on resume?

Hi all, 

I'm looking for advice on if it's OK to combine experience on a resume? I'm currently looking for a second job and was just blindsided by a question, "From your resume, it looks like you've been jumping around facilities. Can you explain that?" 

The gist of it is: I started for an organization in a new grad residency in med-tele (not my goal). A little over a year later, I did a training program in the Emergency Department at a different facility in the same organization. When I was eligible to, I transferred to a different ED within the same organization that was closer to home. After over a year and a half total of ED experience, I was accepted into an ICU position also within the same organization and at my current facility so that I could finally be in my goal specialty (I felt like ICU would give me more options for grad school). I had all four of these nurse jobs listed separately to highlight the different specialty experiences I have and because that's how I learned to make a resume. 

Would it be reasonable to combine the two ED roles since it's the same specialty and job description for the same organization, or would it flag in an employment background check as separate facilities and look dishonest?

I was able to explain in my interview the reasons that I transferred to seek new training or the location convenience and that I loved my current company (I'm looking for additional work, not to leave). I never considered it job hopping because I was only making lateral transfers within the same company. The nurses I've worked with over the years all highlight this as a union benefit that we can easily transfer to gain the experience, location, etc. that we want, but the interviewer did not seem satisfied with this answer. Please advise! I'm just hitting the sweet spot of >3 years of nursing experience that makes my job applications more competitive, so I can't afford to just leave a year or two of experience off my resume so that it looks better,