I forgot to mention that she lives in Tracy, CA where the summers are very hot, 95-106, so she waters every day and the zukes are growing in large pots.

It sounds like they may not be getting pollinated. Are these the first few blossoms? They often send out females only at the start and then start putting out both male and female blossoms later. If nobody in her neighborhood is growing squash and if she has only the one plant blooming, or if insects aren't getting to the blossoms, that could be it. If she is removing the male blossoms to cook with or something that could also be an issue.

Female blossoms are the flowers with a mini-squash for a stem. Males are the flowers on normal stems.

This is my first year with zucchini, so I am no expert. others may have better advice.

But from what I have read here and other places it could be that the flowers are not getting pollinated...though 3-4 inches seems pretty big for that, but maybe someone else knows for sure. Or Blossom End Rot and that is a little different, too much water/dryness or low calcium. I think either of those you can just keep waiting and eventually get something from your plant. Maybe others have some other ideas as to what the problem could be? But in the mean time maybe you could look up pics of those and see if it is similar to what you are seeing.
Hope you get some zucchini!
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How large are the pots? I'd be suspicious of anything smaller than a half-barrel for standard zucchini varieties.

Are the pots in the sun? If the roots are getting baked the plants may be under too much stress to produce fruit.

Most of my zukes and cukes are doing Ok when they have shade from the hottest sun.

The problem in coastal CA - is the fog that roles in producing dampness that produces mildew. However, the cucumber yield was great on those planted in high shady areas. Yesterday, was extremely hot - and many of my squash were stressed in areas receiving direct sun.

It may be they are getting too much water if grown in pots. Try giving them some shade on hottest days.

Bejay

I agree with ShawnAnn, lack of pollination could be the problem. Last year, I had several that did the same thing. I first thought BER but after looking at some pictures online, mine weren't all getting pollinated. They were probably 3-4" long when they started turning yellow & falling off.

Here is a link that might be useful: Tales of a Transplanted Gardener

Yup, you guys were right on the money. She only has 1 plant so the problem is most likely pollination. Thanks for all the quick replies.