It's good that she's said she will refund the money.

Anytime there's potentially a dispute, it's always wise to get the communications in writing. E-mail or text is fine. Keep everything for a good couple of years just in case.

If she has verbally agreed to return the deposit at the end of the month, a good way of getting a record is to then follow up with an e-mail or text, summarizing the conversation "for clarification". That produces a trail of events that is proof that she's agreed to return the money. And it holds up in court because anyone claiming that the e-mail or text wasn't the agreement would immediately respond and say so. A lack of reaction from them is viewed as the summary being an accurate one.

Hopefully you get the money returned. If it's not too big a delay since you had this conversation with her, try and think of a way to get it in writing without it seeming like you are gathering proof.

Just needs to be a few lines :-

"Hey X,

We are just trying to work out our finances with the switch of child care providers. I know we have agreed to getting our deposit that is credited to the final month's fee back at the end of the month, not the beginning, but could you indicate the approx date we can expect that $XXX.XX back in our account so we can plan for our outgoing costs to happen after the refunded fee comes in.

Thanks"

Something like that should result in either a date, an approx date or even a statement that she's not sure when you will get your money back. All of these provides you with confirmation that the money will come.