Not quite sure if there’s a shortage of stories with Hermione digging at two guys… the obvious ones would be flirting with Harry & Ron at the same time, the bar for setting that up from canon is pretty low. If you pair her up with Fred… well, twins could play the bait & switch game. My existing fanfic (explicit version) on AO3 is filled with Hermione tangoing with Harry and Ron at different points in time (even some Harry/Ron)… it’s not a finished chapter in that story until at least one todger expresses itself.