With my babies, I have a simple activity I do to help them get used to recognizing beats. I have no idea how effective this is at teaching it, but they enjoy the activity. It is really hard to measure results in a baby. With toddlers and preschoolers, you see them responding quickly to things they learn. With babies, you see the fruit long after you sowed seeds.
Your baby needs to be old enough she can sit unsupported. For most babies, this happens around 6 months.
Start the music playing. Sit baby in your lap, facing you. Move your legs up and down--gently--to the beat of the music. I also like to sing along. My babies look at my face and smile away. Toddlers will enjoy this, also, as well as your preschooler when the mood is right and if you are in the mood for a workout.
This is something you can do almost anywhere, so long as you are willing to sing. You can be the sole source of music for this activity if you want to. I even do this at church as we sing the hymns. When Brayden was a baby, this was the best activity to get him past that fussy hour close to bedtime.