Wow, I can't believe I disagree with you two on this. LOL. Well, I don't totally disagree, but my first instinct when reading the post was a kinda ghetto neck-roll, frowned face, hand-on-hip type of reply... If I'm picturing this correctly, this is a sister coming to you on Sunday morning saying "can we sing so-and-so today?" or "Mother Parks would like us to sing such-and-such today." In the first case, I would comply ONE time and after that, only if the Holy Ghost led me to comply. I would tell her, "I'm sorry. Maybe next week," and walk away. But honestly, I wouldn't really be in that situation because I'm a planner so by Sunday, I would've already prayed about the song list and planned what we're singing. Same thing goes for rehearsals. I'd already know what we're rehearsing, so her request would probably be too late.
Now, if this were a one-time thing (which you made it clear that it's not), I wouldn't mind obliging her. But over and over? Heck no.
If Mother Parks was sending a message, I would sing the song she supposedly requested, then go over to her after service and say "so I heard you put in a request for 'Pass Me Not', did you enjoy it?" That will let you know whether Mother really requested that or the sister just lied.
I'm just cautious of people trying to control my operations, and after you give them a little leeway and it gets out of hand, you'll be the one having a hard time killing the monster you created.