Visitor Visa for in Law

[palaremzi]

My mother in law had a 2 year visitor visa, which ran out recently. She made two visits with that visa:
Visit 1: March 1 - June 21, 2016
Visit 2: June 12 - Oct 24, 2017
The last visit was due the birth of our second child and it took a bit longer.

Last week our GP referred my wife to a specialist, and they suspect skin cancer. We are both British citizens but have no family here in the UK and in case she needs in-hospital treatment, we need support. I thought about applying for another 2-year visitor visa for my mother in law, but considering her last long stay, and the potentially long duration of the treatment, I am not sure if they would grant her the visa.

Is there's a risk they'll reject an application so soon after the last (long) visit, even if the reason is a medical emergency?