Mental health and friends

I feel really bad at the moment for not being able to dedicate more of my time and effort to supporting my friend. She's having a really tough time.

Thing is, I'm doing pretty terrible myself. I work a full time job and am responsible for pretty much everything in our shared house, finding a house for the new academic year and figuring out my dissertation.

How do I juggle healthy boundaries with still being a good supportive friend?