Since the OP has already bought the ticket, the optimal choice is no longer an option: just redeem an award ticket in U inventory for no-status, infrequent flyer moms. Just 50k miles round trip. Or if you really like mom, try to get a 65k mile Z award in First Class. Both are better deals than purchased ticket plus 30k miles plus co-pays.

But since the OP has already bought the ticket, I recommend using the mile plus co-pay option for mom to maximize the chances that both are sitting in biz class. OP can play the upgrade lottery and as an EXP, stands a fairly good chance as a solo. An EXP trying to upgrade a companion has a lower chance of success.