J.D.
When a baby sleeps in a swing, it is because the motion is similar to the womb. It is comfort... Do you swaddle your baby? I would purchase a SwaddleMe blanket from Babies R Us. They make them in 3 different sizes so they should fit your baby if she is of normal size. If she hates a swaddle, they make blankets that allow her arms to move also that my daughter loves at 6.5 months. The other thing is that your baby likes to sway to get to sleep and probably white noise. We also used a teddy that played womb sounds at that age.
I will say that there is no magic to getting a baby to sleep. Each one has their own needs, you just have to figure out the right combination and stick with it. Make sure you have a routine for bed time.
My daughter Elizabeth eats, plays with Daddy while I make dinner, gets a bath (because she loves a bath and I ok'd it with my ped), gets a full body lotion massage and dressed for bed, gets a bottle, plays with Daddy and wears herself out until 8 pm, snuggles up with Momma for 15 minutes with another bottle, I take her and zip her into her blanket, I lay her down with a song and she goes to sleep. Her nightly routine starts at 5:30 each evening with very few variations. Most of my daughters day is on a set routine since my husband has blessed me with the ability to stay home. Babies like to know what is going on it keeps them happy.
This is what works for us. Find what works for you... These are just suggestions and I hope they help. Good luck!