The difference is easier to see if we switch to the third person.

If Candi's late mother were here, she could tell us the answer. This construction is used for untrue or hypothetical situations, or ones I consider unlikely to be occur.

If Angela was at the library this morning, we'll be hearing from her very soon. In this case I don't know whether Angela was at the library this morning or not.

People who start tossing round terms like first, second, and third conditional tend to forget that it is possible to make conditional sentences about the past, the present, or the future, and use any aspect (simple, continuous, or perfect) and not know whether the event happened or not. They then come up with inaccurate rules like always use were not was after if.

In casual conversation this distinction is starting to fade, and "was" is often used in both the above situations.

Bingley

Bingley