Ok, I'll throw my two cents your way.

First of all, a BP is a great choice based on what you're looking for. You can't go wrong with a corn or hognose either (don't rule out Kings at some point either if you decide to go the colubrid route). As far as a BP goes, you should have no problem finding a beautiful example with all the morphs out there (choosing my next morph is proving to be pretty difficult, I want so many!!!) who also has a docile temperament.

As far as you gf's concerns: I wouldn't be worried about the snake pacing it's enclosure. If the husbandry is right it won't pace at all. It should explore at night a bit, but will mostly stay hidden the majority of the day. I definitely wouldn't worry about the cockatiel either, not a BPs flavor therefore not a concern. I keep my snakes in the same room with my ferrets and they are ALL perfectly fine sharing the room. They obviously don't come out of their enclosures at the same time. I've also heard of many people keeping mice and/or rats in the same room as the snakes with no issues.

To address the "not much to do with snakes" issue, she's pretty right about this. There really isn't. BUT, they are fascinating animals if that's what you're looking for. My snakes come out for at least a little while most days. Some days my BP will be hanging out with me for an hour or more, my adult King was out with me for 2 1/2 hours the other day just chilling, exploring, hanging out. Most handling sessions are shorter, especially towards the beginning, though. There are, unfortunately days when you really CAN'T do anything with your snakes because of feeding schedules or shedding. That's when having more than one is nice. But the fact remains, they are often nicknamed "pet rocks" for a reason. BPs do spend MOST of their time hidden in nature, and if well cared for they will in captivity as well. Another saying you'll hear often when regarding BPs is "a hiding ball is a happy ball".

To touch on her father's luck, I have no idea what species he was keeping, if they were kept properly, etc... so not much to say there.

If you're looking for a pet that requires little daily maintenance, a BP is a great choice. They do require daily checks, but spot cleaning and changing water are all you need to do "regularly" once your setup is correct and dialed-in (this may take some time and trial and error). Do yourself a favor and do your homework and have your setup ready BEFORE bringing the snake (or any pet) home. This will save you a lot of potential headaches and stress.
Aside from spot cleaning and changing water, feedings are weekly (easy enough) and full enclosure cleanings are monthly give or take. Pretty simple. However, don't take the simplicity for granted and go days without checking the setup. I check all of mine daily.

I almost forgot to touch on the wasted food/money issue... Yes, refusals happen, sometimes week after week after week. That can be frustrating, but if you have more than one snake on the same size prey the other snake will almost always eat the first snake's refusal. Schedule feedings accordingly and eliminate waste.
Oh look, I just found you another reason to have more than one snake

Anyway, my GF was against me keeping snakes for a while, but she was afraid of them. I have since introduced her to snakes, helped her to understand them rather than fear them and she is now cool with snakes. WE have 4 right now and more to come when the time is right. She absolutely LOVES my adult Kingsnake.

Don't bring a snake home one day and ask forgiveness, that's not fair to her or the animal. The enclosure should be set up and ready to go before you bring it home, which would (hopefully) tip her off anyway. Just ask her again, do your due diligence and show her some concrete facts about BPs that will sway her and you should be fine. If she continues to say no, do the right thing and listen.

Anyway, good luck!! We're here if you have any other questions. Hope I helped you out a bit.