I agree with Meaghan on this one. I owned a local playgroup for years and these things do happen and can come up. It is proper etiquette to replace anything your child breaks--whether that is a toy or a bowl.
On that note, She may have waited to call so not to confront you in front of everyone, which would have been in very poor taste, and not proper etiquette. Or she wanted to make sure it was your child by asking a few of the other Moms some questions. This is just speculation...
In order to fix this issue we had it in our rules that if you or your child broke an item you were responsible for replacing such item. This also encouraged certain Moms to pay more attention to what their child was doing, instead of ignoring them and using this as "chatting only" time.
You have to remember that some children are easy on toys and some are rougher. This toy may be something her child plays with all the time, but did not break because they were easier with it. Most parents do not expect to have people over and leave them with broken toys, spills to clean up, and a tornado of a home to clean up. It's just plain manners to clean up spills your child makes, help to pick up the toys used, and to replace anything that your child broke.
I know that I have gotten very annoyed when cleaning up to find broken toys that no-one admitted to me before they left to have been broken. And if i knew who had done it, yes--I would have asked for it to be replaced if it was about $20 and up. Toys are expensive--and some families have rules about no new toys unless it's your birthday or Xmas or other major holiday.
Sorry to ramble, but i have encountered this a lot with being owner...Many members came to me upset because they had no idea who broke it, and it may have been expensive, important to the child, or just the principle of the matter.
I had a member who even posted all the broken items after her play date and just asked if anyone had any idea who broke these. No-one fessed up, but a few chipped in money to replace the item, just in case they blinked at that moment.
Accidents happen--we can not see everything our kids do--but we can make sure the waters stay smooth by helping to correct any oopps! our kids have. :)