have been 問題

If she wins, it will be the first time a woman has been elected president.= correct as it will be = tells us that will happen in the future.

or

If he wins, it will be the first woman elected as president.

A woman will have been elected president.

It is idiomatical to use the present perfect after the time phrases, such as "This is the first time ..." or "It is the second time ... " etc.

The rationale behind is:
~ we use present perfect to refer to something we experience;
~ we use present perfect to express repetition of actions (first, second, third, ...).

The difference scenarios:

1. Factual (she wins / has just won):

(i) a woman has never been elected president before
~ This is the first time a woman has been elected president.

(ii) a woman has been elected once before
~ This is the second time a woman has been elected president.

2. Hypothetical 假設 (if she wins): conditional-1 sentence

(i) a woman has never been elected president before
~ It will be the first time a woman has been elected president.

(ii) a woman has been elected once before
~ It will be the second time a woman has been elected president.

2015-04-15 01:01:21 補充：
而唔係未來完成被動?
In English expression, we always focus on the main idea (the first time).
Compare:
1. It is the first time a woman will have been elected president.
2. It will be the first time a woman will have been elected president.
3. It will be the first time a woman has been elected president.