Speaking from experience, as someone with inattentive ADD and other issues with executive functioning, I'd say let her hit rock bottom. Don't bail her out. It sounds harsh, but, speaking for myself, the best way for me to learn was to fail...and then fail again until I learned not to suck or to suck in different ways. When my parents bailed me out, though, I really didn't fully learn the lesson beyond being frustrated and ashamed with myself and hating myself for getting into that situation in the first place. I didn't ask them, but they got the bills in the mail, the inevitable fights would erupt and then they'd pay it off.
What broke the cycle was when my parents stopped supporting me after they found out I'm gay. I hadn't finished school yet; I was recovering from a major depressive episode and had come home because the school forced me to take a leave of absence. I decided that success was the best way to say "fuck you" to the sperm donor, who precipitated the decision. It forced me to cope with grownup responsibilities, like paying rent and utilities every month and on time or face the wrath of my roommate(s) or be evicted, paying my own cell phone bill, paying a car note (not Mustachian, but I learned from that!), and so on. I went on to finish my degree after waiting 2 years to go back to school so I would be considered an independent student for FAFSA purposes. It's been over 6 years since all of that took place, but in some perverse sense, being kicked out was one of the best things that happened to me, especially now that I see my younger (24 y/o) sister making similarly stupid decisions with her money and still being bailed out and coddled by our parents. She happened to get a well-paying job right out of college, so she isn't quite feeling the impact of her choices yet, but I have a feeling that it's coming. I wish her no ill will, but I'm not stupid either.
I'm not saying that you should kick her out, but putting some external pressure on her (assuming she doesn't pay rent or contribute to household expenses) might give her more of a sense of urgency. IMO, it would be a good idea to offer your help with budgeting and money management, but tell her that non-monetary help is all you can and/or will offer. I agree with ShortInSeattle with regard to giving her a timeline. The worst thing you can do is subsidize her bad decisions and irresponsibility.
As for the ADD, meds can be a BIG help, but for many people they're only half of the picture. Behavioral modification and recognition of deficits is the other half. I'd argue that the latter is more important than the former, but for many people both aspects are necessary for them to be fully functional. While behavioral mods help me, I'm a lot more functional when medicated. I often wish my parents had medicated me as a child, but that's another discussion. For behavioral modification to work, however, the person has to be on board and fully committed to change. Like addiction to drugs, it's SO easy to assume that one doesn't have a problem or to deny the severity of the problem until that rock bottom moment.
Not to be harsh, but IMO, it's not necessarily a good idea to think that the boyfriend should necessarily be a part of her fiscal recovery. It's nice if he is able and willing to provide that kind of support, but I also wouldn't be surprised if their differing attitudes with regard to money were a deal breaker for the boyfriend.
All that being said, she truly might want your help. I don't think there's anything wrong with agreeing to help her, but if she's just going through the motions, she might not learn very much beyond doing what you tell her to do.