Generally agree with some of @MWolf 's comments above. The LORs should come from her PI or lab managers that are most familiar with her work. They will be very important. The faculty will want to know if the applicant is an experimentalist: someone who understands how to design a sound experimental system to test an idea. They will also want to know if she has a curious mind and whether she’s capable of self-direction. She should have experience with common molecular genetics techniques, but if she hasn’t worked specifically with immune cell cultures it won’t be a deal breaker. That stuff can be learned and the right person is eminently trainable.
Most serious PhD applicants have already done a deep dive into the faculty of the department(s) to which they are applying. They’ve read their papers and know the work of the PIs that interest them. Many have already been in contact with the PI and discussed a research area they might pursue - I did, and that was years ago before the internet! PhD programs are limited by the number of students the department can support financially, so the faculty want to know they’re bringing on board students that will thrive in their research programs.