I used to have a stepson with ADHD (worse than ADD, in my opinion) with ODD (Oppositional Defiance Disorder). What you describe in your daughter (forgetfulness, trouble in school, etc.) was also obvious in my stepson, even though he was slightly younger, he was 5-6 when I was married. It is a very good idea to research these drugs because they can have side effects. My stepson changed medications several times due to side effects like loss of appetite and tics, and they never fully went away, regardless of what he was on (I believe he was on Strattera right before my ex and I divorced). I can tell you the tics were so bad with my stepson that he actually had to take other medication at night to relax him and reduce anxiety. Those pills had additional side effects. Some people choose to medicate their child only on school days, others 7 days a week. Sometimes one drug will work, then suddenly stop working and a higher dose or a different drug may be needed. Most of these drugs also take a couple of months to get going in the system too.
Also, please realize that these drugs are not a "cure" by any means. Yes, they can help, but even WITH the drugs, other treatments, like behavior modification or different learning methods need to often be used, because the drugs alone will NOT suddenly make your child be this remarkable student who pays attention in class, remembers all their homework, doesn't fight you for hours on doing one simple page of homework, etc.! I can tell you that with my stepson we did get assistance through the school and they were teaching him and us different ways to make everyday tasks less of a struggle. It was a long process and we weren't close to being there when I got divorced.
You may also want to take time to 1) get a second opinion (ADD/ADHD are thrown about a little too easily by the medical community these days) and 2) do some reading on the subject. Whether ADD/ADHD even exist is still hotly debated. Assuming it is real, however, there are people who swear that there are many other things you can do besides/instead of medication -things like diet and nutrition. Since my ex and I never looked into that, I won't speak to it.
I'm sure the OP knows the drugs aren't a cure all, but is looking simply to get her child some help before she falls too far behind in school. A second opinion may not be a bad idea if you are anxious to get started. Look into the drugs and do the research and learn as much as you can about it. Kids with ADD/ADHD are some of the smartest, most creative, artistic people out there, their minds are just wired a little differently, and knowing how to tap into them is key.