"It is high time we stopped seeing her" would be the correct option.
The phrase "it is high time" is an idiomatic expression that means that something should have happened already, and there is a sense of urgency for it to occur.
The correct verb form to use after this phrase is the past simple form, which is "stopped" in this case. So, "It is high time we stopped seeing her" means that it is overdue for us to stop seeing her, and we need to do it now.
The other options, "stop", "will stop", and "stops" are not grammatically correct after the phrase "it is high time" because they do not use the past simple form.