Not sure what your CT traffic is like, but traffic down here is nothing like where I grew up in NJ.
"Lehigh Flats" is run by the same company as Thorn Flats, but is on the "right" side of the street and doesn't have anywhere near as many problems.
Unfortunately with most of the walk-able-to-campus apartments, they rent out for the next school year back in December/January.
Colonial Gardens is definitely walk-able, and nice enough without too much of a party atmosphere.
Apartments at Pine Brook isn't walk-able, but is on UD's shuttle bus route (when they're running during normalcy; during the COVID-19 shutdown they've all been suspended). Also nice enough without much partying.
Both of those appear to currently have 1-bedroom vacancies or will in the near future, but 1-bedroom apartments are definitely scarce in the immediately campus-adjacent area. She may need to occupy a 2-bedroom by herself, or accept having a roommate.
Places4Students is where the University sends graduate students looking for housing, might be worth checking out.
I can definitely say that the University is down to an absolute minimum as for people they're allowing on campus due to the Corona panic. I'd have your daughter reach out and make absolutely sure they want her on campus now; all regular summer classes are going remote-learning, but there are still a small number of research/labs operating.
Note that I put those links in there, so they should be safe to click.