You go to Phoebe's classes

You decide to go to Phoebe's classes. How hard could it be? Hell, if you make her fail, that would serve her right for being mean all the time.

Walking to your wardrobe and drawers, you select a slightly longer skirt and a t-shirt, the sort of clothing you normally see your sister wearing to university. You strip off your crop top and shorts, revealing your pristine skin and shapely body. Admiring it for just a moment, you pull up and clip on your skirt, and pull on your slightly tight shirt, shifting slightly uncomfortably as you feel a slight tightness around your breasts.

With the easy part over with, you pick up your smartphone and unlock it, trying to find info about where Phoebe's classes might be.

Hold on. Before you continue searching, you suddenly come to the realisation that you'd entered your sister's unlock code without even thinking about it. You realise that even though you can't seem to remember things directly, you have some level of subconscious access to your sister's memories. With that knowledge at hand, you decide to just head to your sister's university and see if you can work out where she goes to class on your own. In the worst case scenario, you can simply return to your original body and let her figure it out herself.