Question about Osteospermum 'Lemon Symphony'

Also seems to be called African daisy or cape daisy. I have them planted in pots, mixed with other things. Specifically 'million bells,' petunias, and verbena. Is there any reason why I should not mix them? The reason I ask is that I bought a hanging basket of LS, petunias and phlox on Mother's day. It was gorgeous! Now it's practically dead. I realize buying them out of the greenhouse is risky, and seldom do it, because they're so expensive. They just don't seem to last very well. But this one just dive-bombed in spite of everything I could do. So I wondered if it was the mixture itself as well as the change in environment.
Also, should the symphony be dead-headed?
Here's a picture of one of my pots.
Thanks for your help.
Genie

I can't think of a reason not to mix them. I would guess it's something else that was the culprit. I would deadhead the daisies.

I started some from seed this year successfully. Now, and in the past, I just throw them in the flower bed.

I wonder if they need to be repotted, or fertilized?