i'm less experienced in the field of tuition and retard seems to have covered a lot of ground in her post.
what i think is, you aren't in the wrong. this mother is a cold assed bitch and i would like to scratch her face.
1. she tries to scam the agency of money and put you in a bad situation ($100 extra tuition)
2. "And, when you was asked to choose, you of course choose a better student that you can teach to improve. And saying that you are not confident is not wrong, but it is how you say it..."
what retard says is true, you were trying to teach the student who needs more help, since you said the em1 girl is smart enough. but you must also realise that whether her mom sends her for tuition is also not up to you. so i guess you were merely expressing your concern that you weren't as good as her at that age - a compliment to the daughter?- but also, it's not good to show your weaknesses to the parent cos they will doubt your teaching ability. parents like to think of the tutor as omniscient or something.
3. she doesn't consider whether you will have time for your own life, or other kids to tutor after tutoring her kids 5 days a week. very inconsiderate of her.
4. she tries to scam you of more lessons by complaining about your 'blunder' (so sneaky)
5. well the tuition agency is also in the wrong for wanting you to lie
however, by pointing out all the things (that aren't your fault), it doesn't solve anything.
maybe you should report this to CASE as retard suggests, i'm not sure about the procedure or anything. she should know more. like retard also suggests, i would also try to drop these kids 'cause the mom is bound to give you more trouble in the future. quitting your agency also sounds like a drastic move, i'm not so sure about that... but they have already put you in a bad situation by making you lie about your qualifications. however, you can't blame the agency solely 'cause they are just relaying what the mom wants -the customer is always right syndrome. blame their lack of rules and regulations against such things and poor negotiation skills. since retard has sufficient friends to offer their help to you, this might not be such a bad move after all.
dear retard, don't be stressed about the money you owe me. i wouldn't mind if you paid it up within the time span of 10 years and then some. even if you don't pay me back, i wouldn't take it to heart 'cause i will know that this money is spent for someone i love (that said, it would be better if you did pay hahahaha). really, you are my closest friend and i don't want you to worry about this. just to let you know, it's $20.50 for the fountain and extra chocolate though. i hope piggo replies regarding her free time...