The title of your post uses the word "discrimination" so let's deal with that next. There are two types of discrimination: legal and illegal. Illegal discrimination is addressed by fair housing laws and involves discrimination based on race, religion, sex, family composition (children vs no children). Legal discrimination involves a landlord or property manager favoring one tenant over another because he or she likes the one and doesn't like the other unless that behavior is a breach of the lease or the statute and you haven't provided any information about what your lease says about subletting.
The lease "ASSIGNMENT: RESIDENT agrees not to transfer, assign or sublet the premises or any part thereof." The property manager is discriminating by allowing other tenants to sublet at will without any issue, so my question would be is that a viable rebuttal or grounds for me to stand on in this situation? The owner is not aware of the fact that the property manager lets the other tenants sublet. She does it because she is unemployed. She pays a reduced rent for being the property manager, and then has the other tenant pay her under the table without the owners knowledge to sublet. Almost living there for free. She constantly has harassed me since I moved in about my age because I am 27 and everyone else in the unit is in their 40's or 50's. This went on well before I ever rented my place out for a day here or a day there on airbnb.

The lease agreement also says written permission is required for any guest staying more than 15 days. I've never had anyone stay more than 3 days at my place. The only reason she knows is because she interrogated my guest when they came at one point when they were walking from their car to my door.

Essentially, if the property manager allows others to sublet to illegally profit from it without the owners knowledge, do they have grounds to treat me differently and evict me for the same thing. If this escalated what remedies would I have legally. I have not spoke with the property manager in person yet, and I plan on contacting the owner if she tries to take action against me while still letting others do the same thing.