If you can post a picture in the gallery of this forum (see small print header) and leave a note in THIS forum to say you've done so, we can look, or else post it using Photobucket or something similar. Otherwise, how good are you at describing... if it has leaves, vs needles, are leaves ? size (compared to a quarter or something), are they round, pointy ovals, long and narrow, tiny, are edges serrated or scalloped, etc? Are needles 1/4": long or 2" long? Are there any flowers? Is the trunk woody (yet)? Smooth or rough? DON'T describe any particular curves that were probably trained into it though by the growers as it won't help at all!

looks like what they call a "ginseng ficus" maybe? I have a new ficus bonsai myself and from what I have read they often respond with dropping foliage after any kind of change.

youll need to post a picture sorry

jc, Take a picture in focus and farther away. Over-watering for one night will not be the cause of your problem. So don't blame your sister. Read up on some insect infestations that occur for indoor plants (it is not uncommon). The literature will have the recommended treatment. Please describe your regular horticultural practices for your indoor bonsai plants. This will help with any other suggestions forum members may have. thanks and aloha.