Yes they do have an elevator but...when we were there for our DS birthday party (sept 19th) the elevator was broken and had not been working for months (according to the staff). Normally the party is held upstairs but I have an aunt that is in a medical scooter and since she was not able to go upstairs, they had our party downstairs. Everyone was very helpful and the party was a huge success!!
Hope you have a great time, I am sure that they can make arrangements for you on the lower lever.