Ok, the things I've found don't necessarily point to my Sunny having a bladder infection...so I'll list what I've noticed here.
Sunny's been drinking a lot, and urinating frequently (which would be every couple/few hours, with my hearing a lot of fluid come out each time, so she's not straining with no or little result, and I haven't seen any blood in the litterbox)
. She's eating just fine, and acting normally (a bit on the sulky side tonight from having gotten in trouble, but otherwise fine). She's been more obstinant than usual, but Sunny has her periods of this anyway, so I don't think much of it. I also didn't think much of her urinating and drinking habits, as I've been home more often the past couple weeks, so it might just be that I didn't realize how often they "go". (Another thing to take note of is the fact that we haven't been refilling their water any more than usual...so it could completely just be my not knowing how often she drinks/pees.)
I've also noticed her brother being interested in her rear...though he is anyway (we have always had to discourage both of them on a regular basis from licking each other's bums...blech), so it could be my overthinking it (too much time on my hands).
So, the conclusion I come to is this. The things I've noticed may be nothing at all. I can't find a cat health article that lists these symptoms as being something serious. She's eating, drinking, peeing, and pooping just fine, so she could be fine. But I still feel concern, though it could just be paranoia.
Any ideas, guys? I'll keep an eye on her tomorrow and let you know how things are going. I can't afford taking her in if it's nothing, so I thought I'd ask...