Hmm, Sadhna didn't tell the truth today because she was worried how this illness would effect others. As the Doctor said, Kaushi has to be kept from all stress-related issues and finding out that you have a brain clot is pretty stressful.
Maybe she will try and sort out the money issue first because let's face it, had Sadhna told Mamaji, Vinu etc about Mami's condition, the first thing that would be raised would be treatment and subsequently, the fee. Perhaps after finalising the financial aspects (whether that's seeking a loan from Malika or whatever) she will reveal the illness but straightaway will take Mami for the operation.
Guess we will have to wait and see but perhaps this will make Mami realise Sadhna's importance. At the end of the day, Mami is Sadhna's mother figure and she will do anything in her power to save her. Ragini doesn't even want to talk to her and after everything she has been through, Sadhna probably doesn't want to hurt her. Same with Vinu really (with Malti leaving etc). And we all know how much she loves/idolises her Mama...and he too is of ill health.