Contacted my insurance but there is no damage in my unit so there is not much they can do now.
Who told you that? Your agent? Well, it's wrong.
Any time anybody says "You damaged my property, you fix it," that's a liability claim.
Your insurance company should be sending out an adjuster to determine if you are liable or not. Your company has a toll free number to the claims department. Report that the downstairs neighbor is making a liability claim against you.
That being said, my experience as a claim rep tells me that it's more than likely coming from the plumbing that serves your condo unless the spot is close to an exterior wall and leaking in from the outside or from a vertical line that serves all units.
Unfortunately, the way the source is usually determined (if not visible in your unit) is by opening up the ceiling where the spot is and examining the plumbing that serves your bathroom. That's up to her to pay for that. Her insurance will pay for opening the ceiling and restoring it, but not for repairing the plumbing.
Once the source of the leak is determined, if it's your plumbing you get to pay for the repair. Your insurance doesn't cover the repair, but will cover the ceiling if the cause of the leak was your negligence.
If you were not negligent in causing the leak then you are not liable for the damage unless your CC&Rs gives you strict liability regardless of negligence.
Here's another wrinkle. Now that you are on notice of the condition you have a duty to fix it to prevent further damage. If you don't, it's negligence and further damage will be on you. At the very least you should get a plumber into your unit to inspect the visible components of your plumbing for evidence of a leak.
It all sounds very confusing, doesn't it? Well, that's how condo ownership works. Condo water damage claims are difficult.