It can reach their level of sad imo given she also spend a year helping that friend even though she had to do things to Roxas and knew Sora wouldn't know her.
I figure shes over looked because she has no keyblade or lack of development to argue/talk/comment about.
It's maybe exactly that which keeps Naminé from reaching the "same level" in terms of sadness to some parts of the fandom.
Unlike Roxas or TAV, Naminé did
some pretty awful things especially in the eyes of some dedicated Sora fans (in CoM) and Roxas/Xion fans (in Days and KH II).
Her helping Sora directly screwed over both Roxas and Xion, who were not at fault for Sora's condition at all, while she herself was
at fault as she herself admitted even in Coded.
Not to mention the memory mess she created was arguably the starting point for many hurts in the series for characters in- and in general for the series out-of universe.
That she was almost always strongarmed and forced into doing the awful things she did gets all too often overlooked though and some see
her predicament and "level of sad" as less credible/important (or partly deserved) because of the "bad" actions she took.
Part of her being overlooked in terms of her hurt and sadness may also sterm from hers not being made that prominent in the series itself. Days had only two or three scenes involving her.
TAV were practically created just to suffer while Roxas' struggles were made prominent and Xion's was shoved down people's throats so over-the-top that it had the opposite effect on a sizeable chunk of the fanbase.
Compare those to how Naminé is portrayed and it's easy to see why she often gets overlooked.
Naminé arguably also losing her spot in one of the series-important power trios due to Xion's introduction may also play into this to a degree.