Yes. 30 mg. is 30mg. The only thing that could be a problem is if one was long-acting (Mscontin), and one an immediate/instant release (MSIR) formulation. Just make sure that whatever type is prescribed, that both strenghths are of the same animal.
You should clarify it with the drs office just to make sure. That's a big jump. I had problems on morphine, I would be hesitant to offer advise and really it should come from the dr or the pharmacist.
Hope your mom feels better!