These things go in cycles. My college chapter went through a bad period, but now they're doing really, really well. It's tough to watch, but your time as an active member is over and the current chapter must make their own way.
That said, you CAN offer assistance. Get together with a few other graduates from your chapter and send an e-mail to the pres and ask if there's anything you can do to help with (fill in the blank). They may be inspired by your interest in them, which can stimulate pride in the chapter, which leads to better sisterhood, etc..
As a chapter advisor, I've found it's most effective when we (my alumnae chapter) approaches the collegiates with targeted, specific ideas to help rather than a blanket "what can we do?". Taking care of refreshments for an is always appreciated. See if you guys can prepare breakfast for a sister retreat, serve refreshments at rush, host a reception for a recital, etc.. These may seem like small gestures, but they'll help the chapter run more smoothly, and let them focus on other issues. Also, let your PO know that you're interested in supporting your chapter but remember - you're there to support, not to run!