Haha...oh she'd know. She knows more about fish tanks then she likes to know. She doesn't want the 180 because it sticks out farther than the 75. I can keep most of the fish I'm interested in in a 125 or 135. Though if a 180 pops it's head up on CL (my fish tank store of choice) and it's a good deal, I could probably talk her into it. But being safe and planning on a 125.
Splurge where you can. You may be limited on the tank at this moment but things can change. As an example get filters that would easily move toward a bigger tank in the future. Buy quality lighting, etc.