"Her questions, please."
Translation:A ceisteanna, le do thoil.
You're mixing up lenition with 'h' prefixing before words starting with vowels. You can't lenite vowels, only consonants.
When 'a' means 'her', it doesn't trigger lenition, but it does trigger 'h' prefixing, thus 'a ceist' but 'a húll'. When 'a' means 'his', it triggers lenition but not 'h' prefixing, thus 'a cheist' but 'a úll'.