Another update:

I just talked to my dad.
He said that the vet showed him the x-rays, and although the stones aren't as large as her other three were, she has 8 or 9 of them, and even to my dad, just the sight of it was horrifying to him because the stones were that big and so many of them in such a small dog.
The vet also said that she highly recommends surgery. She said that if Megan only had one or two smaller stones, maybe the food can dissolve them, but with the amount and size of the ones she has now, if we wait any longer, one might move out of the bladder and get stuck somewhere and then she'd end up in a critical situation.
She gave my dad an rough estimate of $1,200 for the surgery.
She also said she can do the surgery as soon as possible, like tomorrow or Friday. I don't want to take the chance of Megan ending up in critical care, so I think I'm going to just go for the surgery. I really hope they're going to let me pay it off bit by bit.. It will take me at least 5 months to pay it all off though.
I've had a headache all day today and it's just getting worse. I keep crying and I'm so worried about my little girl. I love her so much and just the thought of her being in pain and possibly ending up in a critical condition or dying kills me.
Please continue to keep us in your prayers and thoughts.
Thank you so much.