If you are at market rent I would not lower the rent. You need to make sure you are making enough money to cover maintenance, CapEx, ect. If you don't like the thought of losing this tenant then I would do a coupon rent reduction plan.
This is something my first landlord did when I lived in an apartment (before I learned about RE investing lol). I signed on for a year lease and they gave me a coupon book allowing me to lower my monthly payments. Each coupon was $100 and there was 12 in the book. Each month I could apply one coupon to my rent saving me the $100.....however....the catch was that if I had to leave and terminate the lease early I had to pay back all the money I saved using the coupons since I did not fulfill the lease term the coupons were tied to. I did this....to buy my primary residence, so I had to cut a hefty termination check. I was able to do it because I knew I would be building equity from here out. Might be worth a shot even if you offer $50/month coupons.