If you are definitely going, it sounds like it would be best to tell your mum very near the time, as you say.
Mum may be only wanting the best for you, as others have said, but if you're determined to ignore what she says there's no point in causing trouble sooner than you have to.
Fruit flies - help needed please.
Army horses loose on London streets
Have any of you got all electric cars? Pros and cons please.