A mí me saca sarna cada vez que vas a verla.

[Premium]

...every time you're going to see her.

Google didn't help me.

[poli]

I never heard the term but I think it means: It really bothers me every time you go to see her.

Sarna is mange. It is clearly a negative reaction.

[ROBINDESBOIS]

exactly

[AngelicaDeAlquezar]

"Sacar ronchas/sarna" means to get sick, like when having an allergy or a bug infecting you. In a figurative sense, it means that the speaker gets angry or extremely bothered about something, and they don't seem to have control over such a reaction.