Dear Washington, D.C. Tenant:
I am an attorney licensed to practice law in New York. I do not practice law in the District of Columbia.
You may or may not have a claim for the $100 value of the walker and so you could try to resolve this matter in Small Claims Court.
You should also look to your lease and to the rules and regulations to see if there is any disclaimer by the landlord of liability for loss to a tenant's personal property unless the loss was caused by the gross negligence of the landlord, and if there is a prohibition on placing items of personal property on the balconies. You should also look to see if the lease required that you have your own insurance to protect your possessions in case of loss.
Your real claim is against the tenant who injured and damaged your daughter's walker because she is the person who performed the act of pouring something over the balcony.
So if you sue in Small Claims Court for the $100 you may think of including the one responsible for your loss as well.
The answer provided to you is in the nature of general information. The general proposition being that you should try to avoid a bad outcome if you can.