Hi Brad,
Sending your friend from the past a Facebook friend request was not necessarily wrong to do.
However, it has been a couple of years since the both of you fell out.
Hence, it is not so surprising that you are yet to receive a response from her.
In a scenario like this, it may be best to ensure that you have a good number of similar interests to hers.
If you have similar interest to hers, she may feel more open to accepting your friend request.
This would be an area for you to look into.