3 Year Old Child, Having Firm Fluid-filled Bump On Elbow, Pain On Pressing. Causes And Treatment?

Hi, My 3-year-old daughter somehow got about a 1-inch diameter lump on the side of her elbow - I m not even sure what from. I noticed it one day and think she probably hit her elbow hard on something. It s not hard like bone, it s more of a firm, fluid-filled bump. It has never turned any colors like a bruise would. She s had it for maybe a week or two now, and it doesn t bother her at all (and she didn t even seem to realize she had it on her arm until I brought it to her attention), except that when I press on it she says it hurts just a little bit. I m wondering what it is and if there s any way to get the bump to go away? Thank you.