Since 12 is 8 x 1 1/2 she needs 1 1/2 time as much fruit.
1 1/2 x 10 = 15 strawberries and 1 1/2 x 4 = 6 oranges.
You could also solve this using proportions:

Cross multiply and get 8n= 120 divide by 8 and get 15 strawberries
Do the same for the oranges:

You can see that 4/8 = 1/2 so n/12 has to be 6 to be 1/2 (or solve it using cross products like I did above).