I have no idea what extraction efficiency you could expect from a cob, but we can’t discount the possibility that the potency is somehow related to all that plant material we smashed the trichomes into, which suggests that a concentrated cannabis oil extraction from a cob won’t be anywhere near the efficiency of buds and leaves still having intact trichomes.
From a medicinal standpoint you’d end up with an oil unlike anyone else’s, we simply don’t know if it’s special enough to absorb the inefficient extraction.
Don’t discount the idea that your girlfriend would enjoy chewing. The high from chewing is amazing, and well worth getting a taste for, IMHO. She deserves to feel this good too.