Sue the city (for the actions of the police department) File a claim with the city once you get a response 90% rejection you have a total of 6-months to file a lawsuit against them.
If she had no proof that your apartment was in fact her residence (e.g., with a lease, driver's license), then the police should not have let her in. They should have tried to contact you first.
You should contact an attorney familiar with police abuses. It is likely that the police will not take your complaints seriously until you retain an attorney.
The foregoing does not establish an attorney client relationship with Attorney Stephen D. Gregg. The information given in Attorney Stephen D. Gregg's answer is not legal advice and is only given for educational purposes.