I would ask why. There should be no reason "your friend" can't completely and thoroughly explain the reasoning for this. I may be a valid request. Or it may be a harbinger of poor business management and practices.
It makes little sense to introduce a middleman if there's no need. There's nothing "wrong" with it, but it seems like poor planning or at the very least poor business management on "the friend"'s part.
If "the friend" is wanting to use upwork so he/she can track expenditures and other accounting details, then your wife would need additional compensation to overcome the commissions she'll be charged for payments through upwork.
If the only reason is due to the escrow payment structure, that can be done without some middleman crowdsourcing web site taking commissions.
If "the friend' merely wants to be abel to pay online electronically, there's PayPal, Venmo, and most banks have their own "cash sending" app as well. You don't need a crowdsourcing site to send payments.
If "the friend" has some ulterior motive, such as building his reputation at upwork, well, that's kind of squirrely if you ask me. Like asking your brother-in-law to give your business a good rating because you know he wouldn't say anything negative. I guess there's no harm in that, even if it is ethically questionable.... except upwork takes commissions from teh worker not the client.
I, personally, wouldn't do it. Not due to anything about upwork and their structure/reliability, but because I've worked for more than 15 years WITHOUT any crowdsourcing site such as upwork. They aren't mandatory by any means. Why give some third-party commissions???