Everyone on this board seems surprisingly hostile
On the contrary, KVal. (1) Many initial posts don't disclose enough information for folks here to access rightly how to respond and (2) we, in general, are alert to boundry making and breeches.
We've worked together for almost 5 years and she is a friend
If that were true, your friend (ahem) co-worker, would have given you more insight into her situation and what she needs/would like from you, or her employer by now. Business wise, and "friend wise", the appropriate thing would be to simply send her a card (if she's given you her personal address) that is sort of neutral yet upbeat and and invitiing, i.e. something that says (or you can write), "Hey, hoping you make it back to work soon. Give me a call if you'd like to meet for lunch before you do. Best regards, _________. When/If you talk/get together, don't prod - let her open up if she wants to.
Your mentor role, I'm assuming from what you wrote, pertained to her career, not her personal life. Is that right?
Whether you are the employer, her boss, or just another co-worker acting on your "personal priority" to help her can expose the company and/or yourself to legal implications if the company, or you, did anything that could be perceived as contributing to her unfavorable state. I am very familiar with working in Finance (my position now is in Internal Controls and Ethincs).
As for understanding what she might be feeling, go to the help pages - read through the descriptions, then imagine how you might feel. Sometimes, many people feel as if they are wired for 110 but have been plugged into a 220 world and they can't keep up. The stress is too much. At other times one can feel as if they are wired for 220 but the rest of the world is opeating on 110; therefore, their behavior seems somewhat frantic - out of sorts, etc. Stress / balance / self-care can be real challenging.
Good luck,
Drew