Originally Posted by Lux Flyer

The information is correct. The only UA-hub that has ITI bag transfer is IAH (MIA does have ITI as well which is why AA was able to do it there). She will need to pick up bags in EWR clear customs and then check them back in on the other side of customs.

Edit: though on the outbound through AA in MIA, it was likely not a true ITI bag transfer. Departures from YYZ to the USA preclear customs at YYZ, so they arrive into the US airports like a domestic arrival and the passengers/bags would have been treated like a US origin where bags wouldn't have needed to been collected.