Hi Tinward. Yes she's in heat. Our first hammy Gizmo absolutely STANK when she was in heat, you could practically smell it from the hallway! They can behave oddly too, like you say ours would get very skittish & irritable, unusually antisocial & very occasionally even a bit bitey. As a female, I'd equate this to PMT, I feel exactly the same at my time of the month!
With the yellow around her bum, please check she doesn't have wet fur & other symptoms of Wet Tail. (There's lots of info on this forum about Wet tail) Don't panic, it might be nothing but please do check, esp. if she's young.