UK Standard Visit Visa Rejected

[KG123]

Hi,
I have recently applied UK standard Visitor VISA for my wife's mother and the application was rejected on 8th December 2017. Visa Officer hasn't convinced with the Financial Circumstances. She has a recently (3 months old) opened Bank Account and we have some Indian currency put aside in the form of Fixed Deposits. Even after we were sponsoring for her travel, and provided her Invitation Letter, the visa officer wasn't convinced. She is single,(widow) with no any assets registered on her name in India. My wife is pregnant and expecting the baby on 31st January. We didn't mention this in the invitation letter. (we bought a new house and in the last invitation letter we mentioned that we want my mother-in-law to visit our new house for the celebrations).
Now after how many days I can make a fresh application ?
Can I mention that we are expecting the baby in January and we need her mother's support during delivery. Are there any chances to get VISA this time with this reason or do they object as we didn't mention about the pregnancy last time?
Please Please advise us.

[CR001]

You can reapply at any time.

Fixed deposits are not considered. Funds need to be liquid.

Without substantial evidence of strong ties to home country, unlikely they will grant a visitor visa.

[KG123]

Thank you so much for the reply.