Are they asking for an additional rec…ie is it even allowed ? What can she add about you that enhances your candidacy vs writing as an alum ? If nothing new, I’d see no reason. An LOR is likely not the reason that you get over the hump. If sue can add to your profile and they allow a letter, then sure. The issue is you won’t know what others touched on so you don’t know if her letter will differ ? And outside of a Dean role, how does she truly know you that deeply that would add value ?