It depends. If Suzy has an ear infection, giving her some of Uncle Derek's Viagra would of course be wrong, however you administer it.
If Suzy doesn't want to take her medicine because she has read that this particular medicine is now thought to cause cancer and is about to be withdrawn, it would be wrong to cause her to take it without her knowledge.
But if Suzy simply objects to the taste of the medicine but otherwise has no objection to it, there is nothing wrong with hiding the medicine in her portion of curry so that she takes it without suffering. If it is the taste that she objects to, and you address that problem adequately, you have solved the problem. (That might be a good TCS solution for medicine taken only once a day, but the child might not want curry three times a day. (See this article for other possible solutions to this problem of horrid-tasting medicine.)
Whether or not you should tell the child that you are doing this is a matter of judgement. I don't think it is necessarily a bad thing not to tell the child. If the child is expecting to taste disgusting medicine, she might well taste it, whereas if she is not, she might not notice. You should of course take great care to ensure that the flavour is masked properly so that the child does not get a nasty shock.
If your child is not currently taking any medication, you might want to raise this issue with her now, explaining all the considerations, and discuss it. She might well like the idea of your carefully hiding her yukky-tasting medicine in food and not want you to tell her. Or she might prefer to know despite the increased risk that she will detect the medicine.