
I've never known a bitch stand for more than 5 days (mating on alternate days), so you've got time yet. Some bitches are very vocal during mating, and it could be that, because they know each other well, he's in awe of her and won't mate her without assistance. After a few minutes flirting, hold her firmly and don't let her chase him.
I'm assuming they're both hip-scored, vWD clear etc etc?