1) Safe? Men and women have been taking it up the ass for millennia.

2) They say if you push like you're forcing a bowel movement it goes in easier. But it may behoove you to let her stretch you a bit if the strapon is of a large diameter. It seems to help my girl.

3) If it's "your" dildo, new, or autoclaved, no need and I'd wash it between uses. If it's been in others, probably yes.