Related policies and regulations:
https://ww2.montgomeryschoolsmd.org/departments/policy/detail.aspx?recID=223&policyID=IKA§ionID=9
https://www.montgomeryschoolsmd.org/info/grading/report-cards-secondary.aspx

From IKA-RA https://ww2.montgomeryschoolsmd.org/departments/policy/pdf/ikara.pdf (page 12)
J. Retaking a Course or Portion of a Course
A student may retake a high school credit-bearing course or a portion of a course,
subject to conditions below. Upon successful completion of the course or portion
of the course, the grade earned by the student may replace the student’s previous
grade as described below.

So yes, if your DD retakes an entire course in the summer, the grade will replace the previous grade.

If my DD fails a class in high school and retakes it in the summer, is the E replaced by the passing summer school grade on her transcript?

If my DD gets a C in a class one semester and retakes the class in the summer and gets an A, do both the C and A show up on the transcript or just the A?

I’m seeing on the MCPS website about grade improvement and class retakes but don’t understand how this works. Thanks.