Technically three is still a group.
A plot idea could be that Lia doesn't go back with Sabine to the stables, and when Sabine and Will wake up, Lia is nowhere to be seen. Neither is Karin.
It does put Sabine as the sole woman traveling with a group of men...
Though without their Cartographer they are out of luck. I don't mind writing a secondary character or letting Will and his little compass try to foot the bill, especially if Lia's things are still at the camp. I would assume that Sabine might figure out how to use Karin's healing items as well.
Let me know - it has potential.