Well, it seems you've not been acquainted with the enema process. Were you given one "this evening" as you posted, or are you anticipating receiving one from your doctor?
Were you told you'd be getting an enema of some sort? If so, you'll possibly be given a laxative prior to any enema being given to you.That COULD be an enema (fleet or small amount by a bag) or given a laxative (orally) that will help you eliminate. Or have you had laxatives in this time of 2 1/2 weeks?
If you are to get an enema, you should have your mom ask the doctor or his nurse or assistant what you are going to have done.