The spots showed up in the last few days; that's why I'm worried. I've had her for about 2 months now and haven't seen the spots before.
Yes, her shell is fuzzy with what I assume is algae. Is that bad? Should I clean her somehow?
I've mostly only seen green algea on snails before myself. It might be ok (if you have more than one eventually they'll clean each other off.)
If it seems to bother her you might be able to try gently scrubbing the shell with a toothbrush?
Maybe the spots can develop later? I don't know, but they look fine to me.