Buying a cemetery plot?

I'm looking for the advice, particularly from older people with kids?

My parents have always been very clear about what they want done in the event of their death. My father and now stepmother, want to be cremated and then once they are both cremated they want to be spread over the ocean. My mother wants to be buried in her hometown where the majority of her family is buried.

Now, they don't have a family plot or anything, and she's never taken steps to secure this like my grandmother did. They just all kinda got in the same area of the cemetery. Grandma had it all bought and paid for probably well before I was born. I've been particularly sensitive and aware of death lately, as my paternal grandfather passed away in February. It's recently dawned on me that when that day comes, I don't want to be faced with having to make sure my mother is able to have her wishes fulfilled. I want to make sure she's got what she wants. So I went investigating and was able to find out that the cemetery where everyone is as (random, it's a very beautiful cemetery. Very peaceful and scenic overlooking the Caprock in the Panhandle of Texas) DOES still have spots available and they are only $200 a piece.

So here's my question - - I want to buy a spot for her, as close as I can to the rest of the family. How do I tell her this? Do I involve her in the process? Do I do it as a weird, morbid surprise? We haven't spoken about her plans in any other way except that she wants to be buried here, and she's in her mid 50's and in improving health, so this is in no way urgent, but I want to be prepared and I don't want to deny her the one thing she always asked for.