How can I ask my former employer for a reference?

[065]

I worked at a large chain bakery/food restaurant last summer. I got along with my managers very well and I worked very hard. It is almost a year later, and haven't been back since. I am now applying for other summer jobs and need to use my former manager as a reference. She doesn't have an email that I can find. I am a bit uncomfortable calling to ask in case she doesn't remember me that well. I know she is on facebook, but we aren't friends. Would it be wrong to send her a message on facebook (in professional language) to ask her if she would be willing to give me a reference if they contact her? Or should I just suck it up and call the restaurant?