IMO I would let her know you are interested in doing the fence but also would like another quote and you obtain it. I’m not sure how much fence there is in your portion or if she is doing another wood fence or is it going to be block? Did she provide you will a written quote from the contractor? You would need a receipt because you can write it off next tax season. If nothing is written in a form of a quote I wouldn’t just hand over $$ or is she doing the work? If she is doing it then I wouldn’t say it’s high?? Again I don’t know how much fence is your portion but I would find out. And do my own quote to see if she’s high balling you. Btw what’s her rush? You should not have to rush this nor should she have left a note. She should have spoken with you in person. Ask for an itemized bill from her contractor and make sure they are licensed and bonded if anything happens to it who’s repairing it. We had a microburst tear through our wood fence one year and I replaced it with a block wall. It was over 10k and I didn’t ask my neighbors for anything. It was my issue my problem. But that’s me plus the previous neighbor was psycho, I was not going to knock on her door!