i wanna ask.

I have to agree with Sarah and McSkipper, I feel like it would be rude to ask.

I can appreciate that your cousin may have the biggest lawn in the family but to me it is no different to asking someone if you can host a dinner party at their home, or use their pool for your kid's birthday party - it is a huge ask and I am sure people would reluctantly say yes by reason of feeling on the spot and not wanting to disappoint the person asking.

Unless your cousin offers their backyard, I personally wouldn't be asking this of them.

I feel like it's rude to ask someone to provide a place for someone (?) to host a shower for you for 60 people. That's a HUGE group for a shower. I think with that number you'd need to be looking at professional services such as a restaurant or meeting hall etc.

It's not at all rude to ask. I'd be honored if my cousin asked to use my yard for their bridal shower. I take that back, I have awful cousins, but most people would be honored. It would only be rude if you just assumed that you were using it, and not asking.