Are you seeing this just first thing in the morning? The rest of her poop looks normal and what's under the roosts are normal?
91 is warm/hot, so she may be drinking a lot more which can cause loose poop and the white urates.
If she's acting normal, then I'd monitor her for a while, check the poop daily - but if she seems o.k. and her bum is staying clean, I'd just monitor.
Ivermectin - save that for later, it can be used to treat mites, it's not that effective in treating worms.
IF you decide she needs deworming, you can find Safeguard at TSC. Use that instead of Ivermectin.