It appears the filter diameter of that camera is 52 mm. The image of the camera at the Amazon product page says "52mmW". I don't know what the "W" indicates, but the 52mm is probably the filter thread diameter.

Additionally, one of the other product images says "52mm Screw Connection for UV Filter (not included)".

Regarding selecting an appropriate close-up filter, you have to determine how close your daughter wants to get to the subject. Close-up filters are specified in diopters, usually from +1 to +10. The diopter value is just the inverse of the close-up filter's focal length, which also happens to be maximum focus distance, in meters, when the diopter is installed. So a +1 diopter has a focal length of 1 meter; +2 diopter corresponds to 0.5 meter; +10 diopter corresponds to 0.1 meter.

Now, without getting into too much optics detail, generally speaking, close-up lenses work better with longer focal-length lenses. The focal length of your daughter's camera is either F=2.4mm or f=5.04mm (printed on the front of the camera). In either case, it's a very short focal length compared to typical diopters you'll be able to find, which only go up to about +10 for consumer gear. So while a close-up lens will allow (actually, require) her to get closer to the objects to photograph them, she probably won't see very much magnification. However, close-up lenses are fairly inexpensive to get into, so I wouldn't discourage the effort. After all, part of the experience of photography is trying things that don't work as well as you expected.

See also the related question, How can I calculate the effect of a supplementary close-up lens (a.k.a macro filter)?