I would just try to be available for her to talk to when she wants to. As a sophomore in college she is an adult. But you are still her parent and you always will be. Just try not to be too intrusive. Just be available.
Like, "honey, I know you are struggling right now. If there is anything I can do to help, let me know. If you want to talk, let me know." You might have to do this several times because sometimes people when they are struggling feel like they are a burden to others.
If grades are slipping, could be that more is going on then just loneliness. Could have a mental health disorder. A lot tends to show up at that age. Young adult.
I'm schizoaffective and while I got through my Bachelor program okay, I found that when it came to my Master program I could only reasonably take one class at a time (I was working full time as well--it was a lot!). It took me 4 years, but I graduated. Maybe she is taking too many classes?
Depression can sometimes come across as laziness, low energy, lack of motivation.
Maybe your daughter needs to take a gap year?
Hope she feels better soon and that you can know how best to help her soon. -- Kit