Is it acceptable to ask my professor for help for another class during her office hours?
This might depend on local custom, but I don't think there is any reason that you shouldn't ask for help. You may be sent to the other professor or just told that the one you ask hasn't the time for you. But asking is fine. 

Of course it is also appropriate to say why you ask the one and not the other. But having a relationship with a professor makes it easier to discuss things with than with someone more distant. 

The professor will set boundaries if necessary. You don't need to be overly concerned with whether you are interfering with other students.