I mean... I am torn here.
On the one hand, I think there are so many ways to be able to feed this snake (as in what you, OP, have already suggested - even finding/paying someone else to feed it, or suck it up and do it yourself because having had the snake for a year, I am really surprised you haven't yet - pregnant or not)...
On the other hand, snakes can go weeks without food. If the snake was just fed prior to your friend going away, I would say 21 days is fine. I don't think it would hurt an 8 year old BP, given that the snake is actually very healthy and in proper husbandry, but I don't know.
They go on hunger strikes for weeks at a time, but because of their own doing.
Like I said, personally I am torn. I think you should try your damndest to feed it frozen/thawed. But I think it would live if the feeding(s) weren't successful.
I am going to add one last thing by saying that I think you ARE a ball python owner. Even if temporarily. I think you did the right thing coming to this forumbut I also think you should learn how to feed the snake. It sounds very possible to me that your friend may not be able to have it back... at least, any time soon.