Riven with svellsongur can i give her a buff and spend buff in a move?

No — the buff from the "Buff me" copy doesn't arrive in time to pay for the "spend my buff" copy in the same move.

Svellsongur does give Riven, Broken Blade a second copy of her ability, so moving her (the move exhausts her) triggers both instances at once. But all Pending items get finalized — modes chosen and costs paid — before any of them resolves (Rule 340.3), and "Spend my buff to …" is a cost at the front of that mode, so it must be paid at that moment (Rule 204.1.c). With no buff on her yet, that copy is removed from the Chain and simply does nothing; the Buff copy then resolves and leaves her buffed but still exhausted from the move.

The version that does work: have a buff on her before she moves (from any other buff source). Then the spend copy pays it off at finalization, and the Buff copy — placed on the Chain last — resolves first, so she ends up readied (or having stunned something) and buffed.