He might notice the taste if she puts it in his water. She could teleport it directly into his stomach, guessing where his stomach might be. Fairies can't die, so even if she messes up...

She tries that, but the magic won't go. 'Inside a fairy' is not a valid teleport-target. Annoying. She'll be spotted sooner or later at this rate. And the risk of the whole endeavor is making her hair stand on end.

She risks him noticing the tiny amounts of juice that are the smallest possible volume of liquid she can teleport, 'ported into his open mouth as he swallows water.