No, the scenario would be: her "high SAC" dive bud experiencing a catastrophic gas loss at the worst part of the dive. Now you have two divers on a partially used sixty-some cuft tank.
If they follow rock bottom it doesn't matter they get up when the first diver reaches the minimum reserve to get both divers to the surface on his tank. Of course that could come quickly on a small tank and reduce the usefulness of the small tank (that has been mentioned many times on SB). Although I have the feeling you know that already...
On somewhat the same topic, I carry rock bottom tables and psi to cuft tables for different size tanks in my wetnotes so it's easier to do correct gas planning with mismatched tanks. Anybody does that or I'm the only one who has problems calculating those in the water?