8 yr old diggin + required placing the can sideways = shallow target
Large can for an 8 yr old girl probably smaller to an adult.
You should not have any problem finding it with the regular 9.5" loop.
The best way to find caches is to differentiate it from small targets. To do this you have to size your target.
example:
a quarter buried at 3 inches will cause SOUND while passing the loop over it of aproximately 10 inches or the size of the coils magnetic field. This obviously does not mean the quarter is 10 inches big. Do the same with all metal mode or the trigger pulled (pinpoint) and look at the screen. The moment you get a Max. reading, or in your detectors case the shallowest reading, when passing the loop over the target is when the aproximate edge of the object starts. Keep passing the loop over the target and notice when the reading number starts dropping, this is the other edge. Repeat in 180 degrees oposite and you have the shape and size.
This is a good trick, remember sound means nothing for size.
The only time I have found the actual object size to be larger than the measurement performed with this technique is when the target is deep, I mean in feet. Even then not by much.
The can will still be there, if you use discriminator you will get a junk signal if any. I recomend you use all metal mode and the technique above. You will still dig a lot of unwanted metal, but much less than if you dont size the target.
If not there, expand search area as mentioned above. If you still can not find it in all metal mode, I ll bet it is not there anymore.
Good luck,
Gilbert