I would encourage you to make sure that the school is taking data now on her handwriting (and all other aspects of writing) development. From the school's perspective, I can see that they feel slightly reluctant to start the formal eval process when she hasn't received formal instruction. But I think what you've described from her and her family history strongly suggest that her handwriting development (and overall written expression) trajectory is not going to be in line with her cognition, or even with normative expectations (particularly for fluency). If they begin taking data now (an easy one would be one-minute alphabet writing probes--start with the letter "a" and write as much of the alphabet as you can in one minute; score the total number of correctly-written letters), on, say a biweekly basis, and track her progress as instruction begins, they should be able to see that her alphabet writing fluency trendline is not as steep as would be expected for a child her age. If they don't have class/grade-wide data/norms on this, you can get a quick & dirty comparison by picking three or four teacher-identified "typical" students from her class and doing this one-minute probe with them each time. (It should be the same students every time, though.) Ideally, they should actually be doing something like this with all the students, as part of a good RTI process for writing, but few schools do. Even if they don't, you could do it yourself, as a means of documenting her rate of growth, with or without normative comparisons.
Here's a link to a pdf on handwriting/written expression standards:
https://www.hw21summit.com/media/zb/hw21/Written-Language_ProductionStandards.pdfNorms from interventioncentral on 4-minute writing probes grade 1-6, using grade-level writing prompts (search interventioncentral):
http://www.interventioncentral.org/...tfy_Writing_Difficulties_NORMS_Table.pdf
