I've been through this sort of thing - had serious issues with both my own family and inlaws and had extensive counseling with both the husband and individually. So I'm coming from a place of experience on this.
You have a wife problem, not an inlaw problem.
Your wife is an adult, right? So why is she still allowing her parents so much influence in her life if it isn't making her happy?
Did she have an agreement with her parents that they would pay for her degree if she did "X"? If so, then she needs to follow through on the agreement, or yes, pay back the money.
If it was just that parents offered to pay with no strings attached, but they're nagging her all the time, then she needs to tell her parents something along the lines of "I am an adult now, and I will decide when or even if I do this. You don't get to tell me what to do with my life any more. I love you and appreciate your help/guidance when I was younger, but you need to back off and stop bringing this subject up. I'm not going to discuss this with you any more, so in the future, any time you bring this up, I'll either hang up the phone or leave."
And then do this.
Each time the MIL starts in on her she should tell her: "I've already told you I'm not discussing this with you. I'll talk to you later." and either hang up or gather her things and leave.
Until your wife is willing to step up and put in place firm boundaries and enforce said boundaries, she's always going to be at the mercy of her parents. She's trapped in a parent/child dynamic and will remain that way - possibly for the rest of their lives. She's the only one that can tell them to stop and teach them that there are consequences (by her leaving/ending conversations). And if they cut her off for that, that is on them and kind of solves your problem in a nice way - no more inlaws! What are they going to do - ground her and take away her car keys? She needs to stop being an ostrich and step up. But yeah, clear and firm boundaries, explain them and go from there.
The other alternatives are that she cuts them off completely - without telling them about any boundaries (which is kind of a chickenshit path - and doesn't give them the chance of changing how they interact and possibly growing into a better relationship dynamic), or you both just shut up and continue the parent/child relationship. Which seems to be working soooo well now. Ignoring and caving in to her parents every whim and allowing them to nag and bully her as an adult is going to wear on your relationship, and could color how you raise your own children. It won't be pretty, and marriages have been destroyed by spineless partners not separating themselves from their parents' influences and establishing themselves as adults in a grown up relationship.
And just my 2¢ - she is like 90% finished with that degree, why is your wife using all those excuses to avoid completing it? You didn't have to get married right then, and even if you for some reason had to do that and then travel "for several weeks" she still could have buckled down sometime in the last YEAR (you're saying "last April" and not this past April, so it's actually been over a year) and got that degree completed. Sounds a bit like some passive/aggressive shit there. As in, she's just sooo busy she can't do it... knowing that it is pissing off her mother. If there is even an iota of truth that some of the delay is due to that, she needs to recognize it and then dump that attitude NOW. And she should definitely finish the degree. Making that a priority is something she owes herself for all of her hard work on it up until now.
ETA: OMG... you just got married this year, and you are now saying in your latest post that you hope she's knocked up ASAP too. You both should just admit that she has no intention of completing the degree. And basically you both need to slow the hell down and get a handle on being married adults too - she can't have a decent relationship with her mother, and can't even stand up for herself, and popping out a kid right this minute isn't going to help matters. You think things are bad now with the wife basically acting like a child putting her fingers in her ears and ignoring the problems with her parents? Just wait until you add kids to mix... your life will SUCK and you and your wife will have so many fights over the inlaws' nagging and demands, and the wife will just cave each time since that's what she's always done. Good luck with that trainwreck.
Slow the hell down, figure out what both of you want, and then be honest with yourselves and her parents and set some damned boundaries. She needs to do this: as in "mom, I'm not completing that degree, so stop talking about it." and then enforce the boundaries NOW.