I am not familiar with children's disabilities and how it impacts them, I am familiar with disabled adults (as in psychiatric disabilities). Can she have enjoyable interactions with others such as yourself, other adults, other children? Animals? Inanimate objects? If left alone with some toys around will she play with them? Does she show interest in music? I have a baby and he shows a lot of interest in those educational type baby shows they have on Nick Jr and PBS. The one's with different interesting looking characters, often animals with odd shapes and bright colors, where they teach 'lessons' around friendship and more general learning such as numbers and letters, etc. What is her age?
Something I have noticed is that babies love other children. They (and pretty much everyone) loves, even thrives, on attention. My belief is that everyone (save some disabled possibly) has an inate need for attention. I believe that prisons are filled with adults who did not get positive attention as children. They needed attention and learned that the only way they were going to get it (long before they were old enough to 'process' and 'understand' this on an intellectual level) was by doing something bad or wrong. Mommy and Daddy didn't jump up and down and spend ample ammt's of time telling little Joey how great he was and how proud they were of him every time he used the potty and every time he drew a picture, every time he did his homework, etc. Those times he was ignored or treated in a perfunctory manner. But when he stuck his toung in a wall outlet he got their attention "NO!" maybe with a slap. Play nice with his sister he's ignored and his parents are content that neither child is bothering them. Pull his sisters hair, she screams, he gets their attention "NO!" "You damn bla bla". So it gets ingrained in their psyche negative behavior gets attention. As they grow older the behavior is delinquent, etc, etc...
So giving children attention is always a great idea, especially if it is to praise them when they are doing something good, something desireable, something that will help them be a decent and responsible human. Look for opportunities to praise positive behavior. Go over the top with it.
What's the age of the child? What is the disability? Will rolling a ball back and forth sitting on the grass or carpet make the child entertained? Going by the water? Is she old enough to enjoy flying a kite? Is she able to do learning activities like making puzzles, using building blocks or whatever? Can she push a doll in a baby carriage herself? Is there the possibility you could find a resource where others are caring for disabled children so you could come together and explore possible play dates? Just a few thoughts...
Drawing, painting, listening music etc.