Zebra Finch Egg Binding Prevention

I have a zebra finch who became egg bound yesterday. I don't know how old she is but I think she's pretty physically mature. I've had her 6 months and she had her adult markings when I got her.

She laid 2 eggs about a week ago without a problem. There wasn't a good nesting place in the cage because I wasn't planning on breeding them. (I'm not 100% positive my other bird is even male. He's a zebra finch but he doesn't have the regular color pattern so I'm only guessing. I've never seen them mate, the only reason I think he's male is that he chirps and trills as well as beeps.)

Anyway, she seemed distressed when the eggs she laid last week ended up falling on the floor and tried to make a nest under the water dish. They have a nest that is basically a big cardboard tube with straw and the inside is flat and slopes down a little, so while they can sit in it happily the eggs rolled out. So yesterday I got them a real nest and a new toy and a different food dish and thoroughly cleaned and rearranged the cage.

They get a finch food mix with seeds and pellets that does have an expiration date (which isn't for 6 months), they have a cuttlebone, and they get a daily egg/eggshell/vegetable mash that she has been eating like crazy since the first eggs. I also add Avitron vitamin supplement to their water. It doesn't have an expiration date but I know I've had it for over a year. I don't know if it goes off or stops working.

So she was egg bound and I tried the oil massage and the soak in warm water and nothing was working. The bird guy at the pet store suggested holding her over steam and I found a youtube video of somebody helping an egg bound parrot that way. I tried that very carefully and we got the egg out with no breaks. This one was significantly larger than the earlier 2 she laid. It's been several hours and she seems fine now. Still tired but I can't blame her there.

My question, after all this, is, is it still a diet/vitamin problem? If so what should I change? Or is it maybe stress related since I disturbed the cage too much yesterday? Bird guy at the petstore said they probably need a full spectrum light to make full use of the vitamins and calcium I'm trying to give them? I want to prevent this from happening again.