Politicians do not always present opinions which are their own. They try to present opinions and policies which may attract votes, and sometimes use controversial stances on certain issues as a way of gaining visibility (if you want votes, the voters have to know you exist and are different from your opponents). So:
It's not about what Le Pen thinks, it's about her presenting policies which may attract votes. Maybe she really believes in the need to improve Franco-Russian relations, but that is not important. Part of the French public wants to abandon the economic sanctions against Russia, since the Russian counter-sanctions are hurting some sectors of French economy. Another part of the French public wants to decrease the risk of possible military confrontation with Russia. Yet another part of the French public doesn't like US interventionism (blames it for the current European refugee crisis) and, in light of the evolution of the Syrian conflict, sees Russia as a natural counter to it. Le Pen decided to offer these voters what they want (apart from other things like the destruction of EU and islamophobia).
Yes, Trump's offer was in some ways similar, though he didn't talk much about the sanctions - US-Russian trade is miniscule compared to EU-Russian trade - and concentrated on what the US public fears post 9/11 - international terrorism. He argued that by cooperating with Russia, US would be able to more effectively fight ISIS and other terrorist groups, which would lead to decreased threat of terrorist attacks on US soil. The possibility of military confrontation with Russia is also a significant issue for US voters, if they don't know anything else about Russia, they know it's got nukes. Also, the currently trending russophobia is seen by some as dangerous to US democracy.