This is not uncommon, especially for the begining of 4th grade when students make a leap from learning to read and write to reading and writing to learn. That requires a different skill set.
The skills that make her an exceptional student are not the same skills that she uses to stay focused or to work independently. The skills that it sounds like she may be having trouble with are those of executive function, and very smart people can have this issue and still be very, very smart.
Mom should speak to the teacher about what is going on in class, as the year goes on, many of these issues may overwhelm her ablity to cope with the new challeges of 4th grade, and Mom does not want it to get that far. Home is not going to be the only place she has this issue, so a close working relationship with the teacher is going to be essential and Mom should meet with them ASAP to discuss what she is seeing at home. A neuropsycholgical evaluation would be the best way to pinpoint exactly what will help her to learn more effective executive functioning, as a very smart child who is probably not showing significant educational need in school, Mom will proably have to pay for this evaluation privately, but it is not out of the question that the child would qualify for something called a 504 plan and some assistance with these issues based on the private evaluation.
Especially if Mom is spending a great deal of time (more or less-acting as her daughter's executive functioning) and that this is causing tension, she should assume that it will only get worse without targeted interventions (because it will) so first, she needs to identify what is really going on via evaluation.
M.
Just a note, no child should be put on ADHD medication without a full psycho-educational and medical evaluation, and medication is only appropriate as a part of a comprehensive theraputic treatment program. The concept that too many children are improperly diagnosed with this condition is inacurate and damaging and may discourage those parents who are seeking advice about the appropriate way to treat this very real, very serious, very dibilitating, and very treatable condition.
That there may be practitioners who diagnose inapproriately does not negate the need for parents to seek proper evaluation and standard care. Please learn to differentiate between the two categories of diagnosis. The vast majority of children with ADHD have a full evaluation that is entierly different than the off handed insensitve commentary that is repeatedly suggested on this site; most parents do not settle for a five minute convertation with their pediatrican and a pill. That is ludicrous, and those who do need to come here and learn how their child was short changed, so that they can seek appropriate standard care. Parents who did "due dilligence" and sought out a full evaluation have nothing to be ashamed of, and parents who have been given less than standard care from an irresponsible physician should not feel guilty for not knowing any better, and should have the opportunity to seek out a more intensive evaluation without then questioning their own motives for doing so; no parent is looking for a pill to shirk thier responsiblity to be a parent. Please do some more research on how ADHD is diagnosed, what the treatment really consists of before you monger this myth any further.