You cant do it at this point without losing a year of eligibility now that she is already in high school. Players who want an extra year repeat 8th grade before HS starts. Here is one quote I found "From the time you first begin ninth
grade, you have four years to complete your core course
requirements. THIS IS CRITICALLY IMPORTANT: if you
repeated a grade, your window for completing all requisite courses closes at the end of your junior year." That is the first issue with repeating a year.The 2nd issue is that your grace period between graduation and starting college starts at the time of expected graduation which would be the end of her junior year if she repeated a grade. D1 only has a grace period of 6 months and D2 12 months. What that means is she can only compete 6 months after her expected graduation date. If she repeated a year and competed the only time of her "new" senior year, she would lose a year of eligibility. If she graduates on time and takes a gap year, she still cant compete after 6 months or she loses a year of eligibility. Maybe the best option is to aim for January enrollment and play a lot of tennis from June-Dec after graduation. The problem is coaches will recruit her based on the level she is spring of her junior year or fall of her senior year. She could get a preferred walk on spot later. Another option is to start at D2 and transfer to D1 which might work if both universities are in the same state with similar gen ed requirements. She is too smart to want to start at JUCO and transfer.
Here is a NCAA eligibility fact sheet on delayed enrollment
http://fs.ncaa.org/Docs/eligibility..._Certification/Delayed_Enrollment_Webpage.pdf
I would encourage you and your daughter to consider D2 or D3. If she is struggling to manage AP courses, SAT review, and regular HS courses, she may struggle with the demands of D1 tennis. I dont know if she is looking at Power 5 D1 colleges or midmajors. Many P5 colleges travel across the US and miss more school than midmajors. Maybe a MM D1 is a little less demanding but NCAA estimates that D1 tennis athletes (both P5 and MM) spend 32 hrs a week in season in athletic related activities. You may hear 20 countable hours but a full day of competition in a fall invite or in a spring doubleheader counts for 3 hours max, plus volunteer work, compliance meetings, travel, etc dont count in the 20. It is like have another job besides school. Players at D1 usually can have only 2 out of the 3 successfully: tennis, academics, and social life. Most of an athlete's social life revolves around team and other athletes-not much time for other school events. On another site, coaches complain about girls' quitting teams to join sororities. It may be possible to balance sorority with D3 tennis but not D1.
I understand where you are coming from but if you miss the 8th grade window, you are stuck. My son was 5'6 115 lbs at the end of his freshman year of HS; during hs jr and sr years of HS he grew 8 inches and gained 65 lbs. We would have loved for him to have had an extra year of juniors at his full size, especially since the fact that recruitment was basically spring of his jr yr and early fall of his sr meant he had less than a year of results at his stronger size at the peak of recruitment. We didnt consider him repeating 8th grade because when he was in 8th grade we were not even thinking of him playing college tennis; we just hoped he'd make the varsity high school team at one of the top teams in the state.
You and your daughter may need to expand her list of desired colleges. The P5 colleges usually want players ready to play. She might get a walk on spot on her potential or maybe she would get a girl's full at a MM. Some of the MMs play P5 schools, make it into the ITA kickoff, NCAAs, etc Check this website for the top tennis girls' MM schools and see if any of them meet her academic requirements and if any of them have 7.5s-8.5s playing in their lineup.
https://www.slam.tennis/teams/rankings.asp?season=2019&div=mm&topic=men&week=14 The slam tennis site also ranks the top D2, D3, and NAIA colleges as far as tennis, and you can see their 2019 spring schedule. She will improve faster with her soccer background, and I assume she has excellent footwork. Have her play ITA summer circuit summer 2020. Since balancing school and tennis is hard, get in a lot of tournament play next summer and have her focus on development now to be ready for summer tournament play.