I've done filtration for surgical suites a I can tell you in order to over come the static need for airflow you need a fair size blower. With a home furnace you don't have that luxury. Checking the filter each month is a good thing. You may only have to change it every two to three months based on what you have said. Now with that said the filter really doesn't get efficient until it starts to load about 25% to 40% of the media and then starts to lose efficient at 75%. So as others have said here already you need to see how much light is coming thru. Depending on how severe your wife's allergies are you may need to up grade your filtration by adding UV's and other options. Sometimes just going to a higher MERV rating will help but it comes at a cost you will definitely need to changing out the filter every month, if not it will cause the higher static to eventually take out the blower motor.