It's a boss, so play carefully, ranged weapon (bow or scepter), is ofc the easiest hit while circling her constantly and as soon as she does an attack stop attacking focus on getting away from it, but ultimately that is still by just move sideways from her in that constant circling.
If you must use melee well for the same reasons as above, never be close to her for more than a few seconds to avoid be surprised by an attack, this means that as far as weapon choice harder hitting but slow weapon (ie hammer) is your best bet. Right after she does an attack move in hit once, maybe twice if you are daring, and get the hell out untill she does the next attack, rinse and repeat.
I would say imo it is a little annoying she despawn if you do die to her, having to go and kill SlimeK's yet again to get her to spawn again