Is it a good idea to ask her out in a few days, or to text her after she leaves and ask her out via phone?

So I have a bit of a problem. I was planning on asking this girl out this past friday, but unfortunately, the day i was going to ask her out is the day she wasn't at work (i only see her at work). She was absent because her best friend's sister died the day before. So, it looks like i wont be able to ask her out any day soon. I was thinking of asking her out in maybe a few weeks, but i found out that her last day of work is next friday. I really like her, and want to ask her out, but at the same time I dont want to be inconsiderate. What should i do? I dont know who the best friend is, and i dont know the kind of relationship my crush had with her best friends sister. Any suggestions?