My teen is doing driver's ed over the summer and also says she's not ready to drive. I think she's setting our expectations low if she decides not to take the test for a while.
Others posting here are right -- not all kids are ready; some would like to drive but are frankly afraid they'll hurt someone or themselves or will get in trouble if they damage a car, etc. If kids are feeling those fears you cannot talk them out of the fear.
I would keep having her practice but in areas that are empty and at times when there is little traffic, and would not push her to drive at times and in places where traffic is going to spook her. (We live in a very high-traffic area with a lot of fast, sloppy drivers and I know that already worries my teen--she cannot control other drivers and sees a lot of crazy driving in our very car-centric area.)
I also would strongly consider: Do you have another, smaller vehicle she can use to practice her driving? Or would you be willing to get a used vehicle that she could usef or these next two years of high school? There is a huge difference between a small car and a Tahoe -- just sitting up so much higher and having to figure out where the end of her hood and the back of the car are, compared to the instruction car, is probably worrying her too. I would feel very cautious and wary driving something like a Tahoe the first few times (maybe for a long time) and I've been driving for over 30 years, so I can imagine how a new driver might be intimidated. If she knows she MUST drive the Tahoe, or you tell her that she needs to deal with it, she might be afraid to tell you frankly, "I do OK in the small car but the Tahoe scares me, I don't know where the curb is or I feel like I'm taking up the whole road." Ask her if the Tahoe itself is a part of her reluctance to keep driving and be clear that you're not going to be mad or upset with her if she has issues with the size of the vehicle or feels uncertain about it, compared with the car on which she had her lessons.
I am not sure what you mean when you say that "we end up in a compromising place" because if you're referring to driving, there isn't much to compromise about, unless you mean that you want to her practice and she balks and finds reasons not to go and drive with you--?
As someone who truly believes that basic driving skills are actually basic safety skills, and that folks should learn to drive even if they don't plan to drive daily for work or school etc., I still would suggest that you let her go at her pace. She only just learned, she's two years away from the end of high school still, and she may just not have the attention yet to avoid those close calls. Do have her practice but talk with her -- without urging her to drive, or arguing about why she must drive -- and find out if maybe fear is behind her reluctance, whether it's fear of the larger vehicle, fear of getting in trouble (does she feel she gets yelled at when she makes errors? I am truly not saying you DO yell, but she may feel that way through her own lens), or fear of growing up. I know my teen, who is very mature in other ways, sees driving as the last stop before college and leaving home and she does want to cling somewhat to staying a kid.
Do you drive her to activities and you'd like her to start driving herself? I know a lot of families like that, where the parents are the ones promoting driving because of activities. It happens a lot at my daughter's primary extracurricular, where the older kids drive themselves, and the parents talk about how glad they are to stop making the run so many times a week. If that's the case for you, your daughter may be reluctant to stop having you drive her to activities, either because she likes having that car time with you or because she is afraid to drive to wherever the activity is. She might need to hear from you (IF this is the case) that her activities will continue either way and are not going to go away if she doesn't drive herself there.
I would add that I know some kids who did driver's ed in high school and got permits, but did not get their full licenses until they were in college, and they're doing fine as drivers now.