I want to propose in a spot that a close friend is claiming as her place
How did you find out she claimed the place?
She started acting weird around me after she was drunk.
You should talk to your friend about the place that she is claiming and ask her how she would feel if you proposed there. This way you will be sure that you are not intentionally doing something hurtful to your friend.
I'm going to propose there anyway.
If you were in her position would you not want the other person to ask you before you make this place your special place forever?  She might be totally ok with it and want to help you plan your wedding.