It is rare but not unheard of, so just let her do. More likely is that she's just confused, driven by hormones, they do not plan or think about what to to next, it's not uncommon that first timers get their instincts somewhat mixed up. Especially when there is interference.
When the buck was there when she gave birth it is possible that he tried to impregnate her right again, messing everything up, kits born outside the nest will chill and die if not warmed up soon (a cold kit isn't necessarily dead, it's worth a try to warm them up). Bucks don't care about kits, or if the doe is done or not, there's only one thing on their mind then.
So, if you didn't seperate them while she was delivering be prepared that she might be pregnant again, they are very receptive after giving birth.