Hello,
Thank you for asking your query.
If hydromorphone is tested positive in a individual without any declared drug intake, its suggestive of drug abuse or opioid intake
But in your mother's case, who is already taking Morphoine, a positive hydromorphone does not mean anything ! Because Morphine itself can cause hydromorphone to be positive as both are opioids.
http://www.medscape.com/viewarticle/552168
(Please copy paste the link in your browser.)
Please see the above article for reference. In addition hydromorphone can be false positives in few occasions. Also hydromorphone is usually give as Injections. Putting all these matters into consideration I believe your Doctor might have overlooked/misjudged certain facts. I recommend you to discuss the things with your Doctor (citing the reference article) or to find another Doctor/GP.
Hope this helps