Whether or not the AMC20 "needs to go" is a question that can be discussed for pages. For the "Average Jeeper", the most it needs is a one piece axle conversion, and then usually only after the original axle has spun. There are thousands out there over 30 years old doing fine, thank you very much.
Now if you have swapped out the engine, thrown super big wheels on it and are using the Jeep to climb walls at Moab, you probably have a case.
What is she doing with her Jeep that makes you think the axle needs swapped out? That is certainly more expensive than even if you replaced the axles, welded the tubes and installed a truss. If you do all that you probably have a STRONGER axle than a Dana44, again, for less money.
I'm not being mean here, but I read "new to CJs" and am hearing negative things about something that possibly you have no experience with? How did you come to the conclusion the 20 has to go? Maybe it DOES, but again, how did you get there?
The Internet, bless its heart, has posts of every persuasion on everything. "Don't rebuild that 258, drop a small block Chevy in it instead!" or, "put an AMC 304 in it!" "Purple is the coolest color!" "NO, don't do that, Bed line the outside!"
Lots of people on the Internet would be happy to spend your money! Chances are they'd be happy to sell you the parts, too!
Be careful and study is all I'm saying.