Yay
How much does she weigh? If she's uber uber skinny there's a chance that she won't have conceived again. Also we know that at the most she's only a few days gone so there's also a chance that she might gain enough weight over the next week to have an emergency spay the following week? Eddie gained weight quickly after his op with unlimited pellets and an ickle bit of porridge daily so if she's very thin it might be better to fatten her for a week and then see what the vet thinks is the best option.
How's the other one too, what's her body condition like - similar, better or worse?