It sounds like you would prefer to be friends rather than pursue the open dating option, so that is what I would go for. It's up to her to sort out what is best for her - you have to protect your own interests. It will be much easier for you to accomplish your goal of finding a partner if you are not involved in some sort of quasi romantic relationship with this person.

If you both know that you are not interested in a long term romance with each other (but want a long term romance), then continuing to date doesn't really make sense. It may be a pleasant way to pass the time, but it isn't going to lead to anything -and, like you said, it just postpones the inevitable break up when one of you does find someone.

The criticism sounds a little disturbing. Just because she has a certain opinion about you doesn't mean that everyone does. It can be refreshing to meet someone who is upfront, but also a bit tiresome if it never ends