One thing is to check the saniflow, as nice as it may seem, it will not be a pleasant task, however, if you don't check it and they don't turn up, you will always be wondering. If found in there they can easily be cleaned and sterilised in an appropriate solution.
My first course of action would be to disconnect the waste from the saniflow and place it in a bowl at ground level to drain any water in the pipe. It may just still be n there.
Empty anywater collected in the bowl and then replace it back on the floor with the pipe back in it. Open the machine door and pour a bucketful of clean water into the drum. Gravity will allow it to flow through the impeller/pump chamber and may flush the rings through IF they are still in the system. If they still don't show then you have to start dismantling a few bits starting with the pump housing. Even though you may think you have drained all the water out there will still bit a fair bit in the system so have plenty of towels handy. Unclip both inflow and outflow pipes from the pump and check both openings, also gently spin impeller slowly whilst watching to see if it picks the rings up when the blades go round. You may be just as easy to disconnect the front of the impeller housing and pull it off to look. Have a gentle feel inside the primary flow pipe between the ridges, (This is the pipe that connects from the bottom of the drum to the inlet of the pump and is usually quite wide in diameter and looks like a circular concertina). Still no luck? The secondary flow pipe, (the one that goes out to the waste pipe/saniflow), will need to be examined, and because this usually goes back up inside the machine or may go through at low level then clipped up the outside, it will need to be unclipped and laid flat on the floor. You may be able attach it to a tap and flush through or you may need to feed a flexible wire through with a small cloth attached and pull it through. Still no luck? The agitator bars in the drum can often be removed by forcing them toward the back of the drum and lifting out. You only need to do this to one bar which will allow you to see through to the inside of the outer drum. Simply shine a torch through and move the drum from one side to the other as you search through the gap. There is no need to remove the drum at any stage. The only other place they may be is somewhere between the soap drawer and drum but I'm sure if the fell in the soap drawer she would have noticed at the time. Failing all this then it could mean lift manholes covers and checking the drain runs. Please let us know if you find them.
