I recently filed a small claim against someone w/the address I found for them online. I found this address on two websites for her. She is a photographer.

Unfortunately we recently found out the address doesn't exist - or at least there's no door front to her address. There may be a mailbox at the location though, we aren't sure.

My friend has agreed to serve her tomorrow and knows where she will be at a specific time. The location is not the address we have for her and is not a location we know to be her home. It may be her studio address but it could also be the studio of a friend.

Can I serve her the current SC-100 with this unknown address on it if I do not and can not find out what her real address is..

Put the address you have found for her on the form and serve her wherever you can find her. If it's personal service the address does not matter.

The problem will be if she doesn't appear for Court or you attempt to collect on a Judgment - you won't have a valid address.

She MUST have a business address, whether it's written on her door or not. Where does she get her mail?