You're sensitivity towards her is admirable and very touching

This sounds very familiar and Sagittarian. We are sometimes literally on the crazy treadmill of life but trying to aim for the stars and that ultimate nadir of work or personal attainment and burn out fast. We can feel like we can only reach 20% of out potential... unless we gain perspective.
I too have this predicament and insane drive to achieve (with anxiety/depression.) To reiterate the others, there are likely underlying issues with low self esteem. Perfectionism can be really tough to crack and it might go back to her childhood.
Gently encourage her by telling her she is wonderful just the way she is, that you feel she is capable and competant, but emphasis too the issue of self-care. Be supportive of her achievements too as this is probably an emotionally linked issue.
Maybe buy her some philosophically themed self-care books and meditation. Run her a bath to relax in the evenings.
Make sure you're eating healthily and a smoothie-maker is a good investment.
Something pampering for Valentines
Just be there for a good cuddle/support. Sounds like you're doing a pretty good job!