The Pearl Response.

I think she thinks it will destroy them because if they buy something, and the other one doesn't like it then they will get in a big fight, and then they will split apart and never get married. An example is; if Kino buys something that costs a lot of money and Juana gets mad, and Kino doesn't care she could split up with him, then there would be no wedding. I don’t know if Kino would care, but then realize what he lost.