Nami has never actually rejected Sanji or said no. She's dodged a hug, waved him off, or slipped out of conversations but she has never said no.
On the contrary.
Arabasta - Said she loved him in gag when Sanji asked her when saving them. Gag but still.
WCI - Another gag, but when he takes her words as a proposal, she doesn't correct him.
Gags do add up when Oda keeps doing them.