Hey! Just wanted to say that I totally get where you're coming from, waiting for letter of recommendations is the worst feeling! The way you describe her I don't believe your thesis adviser would be upset with you trying to get into contact, so definitely give them a call just to ask if she is doing okay and if she is available to speak.
If she has happened to drop the ball, I don't think it's too late at all to ask someone else if you have someone in mind. Most professors/supervisors understand that things happen and sometimes need a backup letter of recommendation. You still have a couple of weeks, and typically most professors don't ask for more than two weeks-a month depending how busy they are. As long as you explain the situation and apologize for not giving them more time, I'm pretty sure they would be happy to do it. Hopefully this helps, if you ever need to freak out feel free to PM me!