I've never donated eggs, but I thought I might take a try at responding for you.
First of all, Lupron does not trigger a positive on a pregnancy test. If she did not have the ovidrel at all and no other form of hCG, then any positive pregnancy test would be due to something implanting in her uterus.
Menstrual cycles are a tricky thing. The most regular woman misses a cycle sometimes and the most irregular woman might have a textbook ovulation on the 14th day with a 14-day luteal phase. She's coming down off a ton of hormones, so I personally wouldn't be worried just yet.
Also, Lupron could definitely explain the slower period. Lupron blocks gonadtropins so even though it causes the pituitary to surge the FSH (follicle stimulating hormone) to tell the ovaries to produce mature eggs, the uterus is not getting the estrogen which builds the endometrial lining. No lining = nothing to shed for a period.
I would reach out to the doctor just to find out what to expect. I know women who receive lupron as part of treatment for endometriosis might not get a period for 3 months or more after the lupron wears off. But they're taking much higher doses.
I'm curious to hear more about how this turns out. Best wishes!