Leave her with the HP80; a "slightly longer tank" will do nothing about trim down at her feet.
What is wearing for exposure protection? Why do you feel she has "foot heavy trim issues".
Well, I suppose it would be more accurate to describe her as "hip-heavy". She wears most of her lead in integrated bcd pocket-level pouches and the rest on a weight belt. This pulls her hips down and puts her in a sea-horse posture.
Her bcd has only one cam band and she can't mount her tank high enough to spead the weight significantly far away from her waist.
She wears a trilam dry suit and a lot of lead (~14kg). She is a fairly new diver and has had problems with uncontrolled ascents, so she weights quite heavily. It's all a work in progress of course, but I thought trying a slightly longer cylinder that she could mount higher than the 80s might be worth a shot.