is it odd that my mom wants to set up my cousin with my second cousin ?

The fact that you're questioning the morality of this pretty much says it all. YES, that is an issue. There's more romantic options than with your COUSIN.

I little. Maybe tell her to ask your cousin and second cousin about it, or tell her that it's unusual for this to happen.

Yes

a bit, yes. Well, unless you live in Arkansas.

yes, that does seem very odd

It is odd that you keep asking this question over and over. What is wrong with your cousin that no one but a family member can tolerate being with her?