Your second example is perfectly normal: there is no connection between the uses of will and would in the two clauses.
The first is less good. The first half is hypothetical (would); but the choice of will in the second half means that the speaker is now thinking of proposing as a real possibility in the future. I'm sure that people say things like this - effectively changing how they're thinking of it in the middle of the sentence; but I wouldn't recommend it in writing.
I would also make a couple of other changes, for idiomatic English:
I would propose to her if I got a chance, but I know she would definitely refuse.
Propose requires a "to" for the person proposed to; and reject requires an object, so reject it or reject me; but refuse doesn't require an object, and is more natural here.