ADHD meds do not cause suicidal thoughts as far as I know.
I have ADHD, I struggled for years and years until last spring (10th grade) when I failed two classes because I just couldn’t stay afloat anymore and was immediately diagnosed and put on meds.
My mom has many, many psychologist friends. One of them told her I am the poster child of a girl with inattentive adhd. They’re fine and dandy, doing just fine in school with only a couple of problems, and then suddenly all hell breaks loose and they fail classes out of nowhere.
I’d say put her on meds. If they’re stimulants, then they might cause anxiety, and you do have to be careful with anxiety meds, but ADHD medicine should be fine if you just make sure she doesn’t have weird changes in behavior (but be aware that when ADHD meds wear off you usually crash and get irritable and moody, that’s normal though.)