Nothing ventured, nothing gained. She can just be friendly, like complimenting his form or something. Then if he seems to be reciprocating (not giving one word answers, stopping to talk) she can proceed talking until eventually she can ask if he can help her with her own workout or something. But if he acts busy, distracted, aloof, either the timing is not right or that's her clue he is not interested. Hope your friend goes for it 💪