Is this donkey actually running at you??? Or just coming up to you and being in your face because it wants attention from you?
I am asking this because when a donkey wants attention from you, it will come up close and personal. Donkeys have a very different sense of personal space to horses, or humans. You can see this when donkeys interact with each other - bonded donkeys literally live in each others' pockets. We have three donkeys who, when they want something, will crowd together in a row, side by side, touching shoulder to backside, and crane their necks at us making pitiful noises.
They did the same when we lived in a caravan in their paddock for a few months and they wanted vegetable scraps - all three heads and necks would come through the door together. Horses would never do that, they'd chase each other off!
Whenever our little blind donkey wants a scratch or a social interaction, she comes right on up to me and (gently) burrows her head and neck into me. She will stand like that for quite some time. Donkeys are funny animals, very touchy-feely compared to horses, and much more sociable - this really surprised us when we first got donkeys.
Whenever I cut the donkeys' hooves, the other donkeys will stand right around me and the donkey being trimmed, preferably touching me and each other. Little Sparkle does this even when I trim horses! She will slowly sniff my face while I am working, and even the hoof I am trimming:
I can move her aside with her halter, and as long as she is still able to touch another part of me or the horse, she will happily accept this. She is less enthusiastic about giving up contact altogether. I think it's in their nature to be like this, and it generally doesn't cause us any problems with our lot - they are so gentle.
So there may be some of that applying to your case as well. But, is she actually head-butting you, hurting you, threatening to kick?