DM Adjudication Interruption
Please edit out the results of Harald's spell. Prestidigitation is a utility cantrip, not an offensive spell [no pun intended], and it certainly cannot affect another individual's bodily functions, as he is very much aware. Even if you just want to make the stain appear without the function, Risia will certainly resist. Since it is not intended to be an attack spell, and merely a cantrip, I am inclined to let Risia automatically resist it. [Although, it should be noted for future reference that I have NOT so ruled this time because the actions of the PC in question were altered to avoid that necessity. No DM rulings were made here at all, because a little persuasion settled the controversy.] She will get a saving throw at the very least. We can debate this question in the OOC if you desire, but my ruling issued after any debate will be final. Make your case in the OOC, we'll all discuss, and I'll rule.
Harald may decide that this would be adding insult to injury, given Risia's latest performance check. Harald may be able to best a professional bard fair and square this time, but he shouldn't count on that being a regular occurrence.