Dixieland, even though she is older, spaying will still help, no it will not help right away as she has already started to try and do things a certain way, it is in her mind to do so, however my belief is that spaying a dog at any age, except perhaps over 10 or close to can help with issues such as these that Mini is displaying.
Reason being, get those hormones out of there, we all know how hormones can control our behaviour, just get them out of the way, let her body work them out of the system and she won't have to fight those to behave. Her mind and will to please won't have to work so hard against hormones that are saying otherwise.

Besides, it's better to get any dog spayed for the simple reason of health, too many propblems can occur later in life if not altered.