If you misconnect, the next nonstop is at 4:09 PM. There are connections available via IAH, DEN, and SFO, but a second connection may be a tiring hassle given the wheelchair situation (all a matter of your daughter's situation).
At this point, I would suggest calling UA back and expressing concern about the connection time in light of the wheelchair. Presuming that you are on a standard penalty fare, UA might well waive any change fees and the new flights might be relatively the same cost as what you hold.
Your options, all depending on how you and your daughter handle things physically are to fly into ORD on the last flight the night before and then fly out on the first flight to SNA (what you hold now). There is a Hilton attached by tunnel to the terminal and that makes the logistiics of an overnight manageable. Alternatively, you could depart from DTW just a few minutes later and fly via DEN. That connection is not that much longer, but the logistics of a connection at DEN on UA are easier than regional to mainline at ORD (most likely).
It costs nothing to ask and to specifically ask whether UA will waive the change fee (if there is one). If by some chance, this is a flexible fare, making the change should be easier and cheaper.