I'm so sorry for your friend, and for you.

If possible, ask the hospice social worker for recommendations.

I suspect a funeral home provide this service or recommend an appropriate venue if not held at a funeral home. When my father was in his final days I met with the director of a funeral home and picked a package of services that I wanted. He helped me write up the obit and make decisions for lots of little details, including picking out the casket, where to order flowers, restaurants for hosting the lunch afterwards. The director really had the best advice and recommendations. Then a few days later when my father died, everything was ready and I only had to do half the work. I'm glad I did this because despite all the prep, it was still emotionally overwhelming.

Take care.

OP,

I'm so sorry that you (and your friend) are facing this.

I would consider getting a copy from the library or buying one of this book:

http://www.amazon.com/Unique-Meeting-Wedding-Greater-Washington/dp/1574271199/ref=sr_1_2?ie=UTF8&qid=1350698063&sr=8-2&keywords=party+places+in+dc

It breaks down the locations by how many people it can accommodate, etc.

I really like Hollin Hall:
http://hollinhallweddings.com/

Arts Club of Washington:
http://www.artsclubofwashington.org/

A dear friend is in the end stages of her fight against cancer. She is not affiliated with a church or a religion. Can anyone recommend a tasteful, serene, non-denominational place in DC or NOVA where the family can hold a rather large (250ish) memorial service? She loved gardening, flowers, the outdoors...but would need an indoor place.