Flex bats NFHS rules

[shipwreck]

Here is a scenario I had.
Line-up is:
#01 - Suzy - F5
#02 - Sally - F8
#03 - Fran - F3
#04 - Jan - F7
#05 - Jill - DP
#06 - Deb - F2
#07 - Ruth - F4
#08 - Rita - F9
#09 - Mandy - F6
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#10 - Becky - F1/Flex

First inning is #01 walks, #02 sac bunts, #03 strikes out, and #04 flies out. Other team bats.

Second inning is #05 grounds out, #06 grounds out, and #07 strikes out. Other team bats.

Third inning is #08 strikes out, #09 grounds out, #10 flies out. (Yes--#10, the Flex, batted! The offense didn't attempt/announce any substitution. The defense did not appeal. The umpire didn't notice.) Other team bats.

Fourth inning started with #01 getting a base hit. Immediately, the defense appealed batting out of order.

What is the correct ruling?