Correct approach but careless working on 1:4 ratio. Difference in units is 3 units (instead of 2 units written on the side).
Giving away 1/2 of each set still get same ratio of 4:7 (also difference of 3 units).
When losing 12 notes each, Ratio goes from 4:7 to 1:4, means each set is reduced by 3 units=12 notes.
She had 8 units of $2 notes at first
=8×12/3 = 32 $2-notes at first