Regarding ILR application:

You must not send us your application more than 28 days before the end of your two-year qualifying period. If you do, we may refuse your application with no refund of the fee. However, you must make your application before your current permission to stay in the United Kingdom expires.

Sooooooooo

When A visa will expires on 15 of Feb and She arrived on 25 of March when is the best to apply ??? so it wont be refuse ???

Is the 28 days means when you ENTER UK ??? or before when your visa expires ???