Actually that wouldn't be much of a problem is that happened. When going on EVA the astronauts actually have strips of duct tape already ready to slap on something. Besides I think they do a lot of drills for such an occasion.
You can see the duct tape on the hose where she's already repaired some leaks. I think the real "oh shit" thing here comes from the fact that it's not just a leak, it's a lengthwise splig. It's much more difficult to seal than a simple leak or hole. I think she may also have run out of available duct tape at this point.
I could imagine this eventually happening: *Luna sees something random floating past her ship* Luna: Canterlot, we have another problem. Pony stalionning the radio *with an annoyed tone*: It's always problems, problems, problems! Can't you just call to say hi?