Sansa would have known that LF is a only interested in himself and does not care about her. Although, once Sansa realizes how much of a lunatic Ramsay is, she will probably no longer trust LF as she will assume LF knew that Ramsay was a psychopath and blame LF for whatever trauma she is about to go through.

If Sansa somehow survives this marriage and is able to get revenge against the Boltons and retakes Winterfell. LF will probably have lost Sansas support and perhaps have created an enemy.