I really like both Remus and Hermione, and your summary really interested me.
'She looked at a creature she recognized as a grindylow in a murky tank near one wall; it made faces at her and she glared at it.' This seemed a bit out of character for Hermione; I would expect her to be more interested in the creature than glare at it. Maybe I'm wrong, but I just think that glaring at a creature isn't something that she would do, even if it was making faces at her.
I really liked how you made Lupin so patient with Hermione. He really seems like a good teacher for her.
'“That's part of the magic of the Pensieve,” Lupin explained. “It brings forward an accurate replaying of events from an objective view.”' I liked this part. I don't know if it's canon or not, but I've always thought about this. It has confused me a bit, and even if it isn't in canon, I think that this is a good idea of what the Pensieve does.
'The substance remaining in the basin swirled very swiftly, almost angrily, as though it had been robbed of something, then settled back to its slow pace.' This is a very good description and I like the idea of it. It emphasizes the idea that many magical objects have a mind of their own. I really liked this description.
Overall, this was a very good story. Good job!
I think that this is a very sweet teacher/student moment. I have always loved interactions between Hermione and Remus, so this innocent little scene is lovely. I think that you have Remus’ patience and dedication to his students characterized quite well, and I think that the small detail of Hermione being a detail oriented person was quite clever. Overall, this is definitely a very cute little story.
Very interesting idea concerning how Hermione learned that charm... Well written :-)