While it's true we had no bills to pay as wards of House Fortemps, waitressing isn't a high-paying job (it's minimum wage or below IRL, so I would assume the same applies here) unless it's a posh, upscale restaurant; the Forgotten Knight is essentially the slums' dive bar with an inn attached, so I doubt she's being paid much. Unless she was really raking in the tips and we were gone for a really long time trying to get to Hraesvelgr (a few months, minimum), even without other bills to pay it's unlikely working in the Forgotten Knight would earn enough for extremely rare and expensive materials alone.
Now of course...
... but there's no evidence to support it, so it's rather improbable.