Alice is relayer of last resort, but willing to relay claim for her own swap
Bob only seeks help from a relayer if he does not have sufficient ETH in the receiving account to perform his own claim. He will first try all advertised-in-the-DHT relayers that are not Alice for help relaying the claim. If, for some reason, that option fails, he'll ask Alice for help. At least if Alice is running our software, she will always be willing to help if she has sufficient ETH to cover the relayed claim when the asker is Bob, the counterparty to her own swap.