Any advice?

Courtney • fiancé 💍 Boy Mom 8/2020💙 Expecting #2

So me and my SO will be starting our insemination process November 18th-20th with our sperm donor. Our donor lives 3 hours away so I have to take off of work. My only problem is there's only 1 lady that can cover for me which she is about 65 years old and always says she doesn't know if she can cover for me cause she doesn't know if her body is going to be in pain that day. But ever since I started working there (3 months) I've covered 7 times for her already and she hasn't covered for me at all. So my last option is really just to call in....? But if I do what's an extremely good excuse to call in for 2 days? Or what's a good excuse that will make my coworker say she can work for me? I don't want my boss in my business by telling her I need off for insemination but I think that may be the only choice. Any advice would be helpful at this point.