You can check out the GPP download from the site store. It has the big circuit detailed, which is a tougher tempo circuit and you can see it done there. Keep in mind that this is a girl who was running 52.8 going into that season, although she came here running not much faster than your girl.
You’ll also see hill workouts which you might incorporate as well. If at all possible, do the tempo outside to prevent problems associated with tight indoor turns. Let us know what the pool workout consists of. That might be a good thing but we’ll know soon enough.
We sometimes did longer runs at the beginning of the warm-up for the 400m girls at the highest levels of fitness- 49.91 to 51.08 (3:21:21 for Silver at LA84) in the fall but for a time not a distance- usually 15min but rarely 20min and not really with a set distance in mind (and only on grass!).