Struggling to support [25F]

I just really need advice. I’m in a relationship where I’m trying to support my partner [21F] through a difficult time at the moment with work and mental health. At the same time I’m doing my masters and studying for really big finals the biggest of my life. She feels like I’m not supporting her enough, I make myself available all the time whenever she needs even when I need to work or deal with my own stress and I can’t ask her for help because it doesn’t really help when I do because she’s so stressed out already. I’m someone who likes to talk about things and she always shuts down when she’s upset or when I am. She got upset because I couldn’t when I was ill for a week but at the same time I was feeling really bad and needed support myself but I just felt worse because I couldn’t be there for her

TL;DR I just want to know what I can do that won’t cause an argument so we’re both feeling listened to with limited time on our hands two people with big stresses at the moment