I called out a coworker for skipping work and it turns out she was actually having a miscarriage. What can I do to apologize and make it up to her?

I was working with my coworker a couple weeks ago when she left work without warning. I went to the charge nurse (we're nurses in a long-term care facility) because I needed to find her, and charge said that my coworker needed to leave. I asked what happened because I'd literally seen her half an hour ago, and the charge said it was personal and not to worry about it.

My coworker was off for the week and I had to work with the charge nurse who picked up her line (and charge is a little useless so my work load of course increased and I was frustrated). When I texted her to ask what was going on, are you ok and stuff like that she said she just needed some time and space.

She came back to work the following week and I said something like "Wish I could just disappear for a week, suspiciously right in the middle of peak vacation time." I meant it as a joke, but also sort of like a gentle jab. She said something like "Haha I know, I'm sorry."

I told her that all I was saying is that I know her vacation got denied and it seemed suspicious that she was gone right during the time her denied vacation would have been, and here she is back with a tan.

She said, "I had a miscarriage last week and I needed to leave to go to the ER because I had heavy vaginal bleeding. I didn't plan this. Give me some grace. I just lost a very wanted 14 week old baby girl."

I am fully aware that I am an incredibly insensitive asshole. I apologized and said I was sorry beyond belief but understandably she has been avoiding me and has been very tight lipped around me. We are not close outside of work, but we've hung out a few times. I would say we were good work friends though. I've only known her for about six months or so, but obviously I've completely ruined our working relationship/budding friendship and I am ashamed and disgusted at myself.

I just have no clue what to do or what to say. Should I write her a letter of apology? Should I get her a small gift or buy her coffee this week? I had no clue she was pregnant and I know it's my own fault for prying and for being inconsiderate. I feel absolutely awful.

UPDATE: I bought her favourite coffee and wrote an apology note. We talked after work and she said that she appreciates my apology. Things have been better between us thankfully.