I agree with Rachel. If they really don't want you there, believe me you don't want to be there either. They could easily suck the 'deal' out of your purchase by not approving anyone for your home leaving you stuck with lot rent. If she won't work with you and you can't salvage a working relationship then IMO you should find another park. There will be parks where the manager appreciates the mutual benefit of you working there.
On the other hand it's hard to leave money on the table and you may be able to talk to him/her and win them over. Not only would that make this deal possible, but you could have found your park.
I would have a friendly sit down with her if possible. Maybe she doesn't fully understand what it is you're doing or how it will be beneficial to her. Maybe they haven't spent enough time talking to you to like you enough. You both have the same goal, keeping those mobile homes filled up and the lot rents coming in every month.
If you plan on doing any cleaning up or fixing of these MH's, make sure you let her know that. The nicer the park is the better they look.
Once you do a few deals you will earn their trust/respect and it makes things much easier.
One last thing I'll throw out there, when I met with the park manager for the first time, I didn't walk in as Mr. Wheeler Dealer. I was just a guy that wanted to buy a mobile home, fix it up some, and sell it to make a little interest on my savings. I also paid the $55 application fee so they could run my credit/background and know they were dealing with a decent guy.
Kudos on your $8,500 negotiation BTW!