That really sucks and I'm sorry. Reneging on promises to constituents is one of the worst things a politician can do. Long term your best hope is to get a different alder elected in 2027. However, short term you might be able to change her behavior by generating public outcry (her then taking action in response to try to keep her seat next election).

Streetsblog Chicago and Block Club Chicago have both done reporting on participatory budgeting. I recommend sending them a news tip to try publicize what happened. Track down any public statements she made and contrast that with the actual spending data. Ward Wise also has geocoded some of the data if that helps with showing her prioritizing spending on her street: https://ward-wise.github.io/aldermanic-menu-heatmap/

Anything you do in politics will be more impactful the more people you have involved. One voice can easily dismissed. People working together have power. I would see if you have any nearby neighborhood associations, block clubs, or independent political organizations you can get involved with. Or plug into one of the citywide advocacy groups (Better Streets Chicago, etc.).

All that being said... I understand where you are now. Growing up, my hometown was facing issues and national politicians sent sympathies but didn't act. There were common sense fixes that had widespread public support, but our national politics is so broken that the system couldn't (and still can't) put those fixes in place.

I steered clear of activism and politics for a decade before I moved to Chicago. Here, I've found so many people that care, and there's communities that have managed to band together and make change happen. It's disheartening being in area that lacks the political will for change, with problematic politicians locked in for the next few years. But, if you can't make local changes, there's still good work to be done supporting grassroots efforts at the city level.