When to reapply after UK refusal

Question

My cousin UK visit visa was refused with her one year old son and husband. The reason for her refusal is that she said they are traveling to visit her uncle and they will be spending 21 days. The Eco said she mentioned that she said she will spend 21 days and that spends 50,000 naira monthly on living expenses that they noticed that she spent more than 50000 in some month her bank statement. That her statement is inconsistent. Eco also said she said she will spend 1300 pound for her visit and her husband will support her with 200 pounds. Since her husband has been refused they are not convinced if she will get the 200 pounds. Her son was refused due to his parents refusal. She wants to reapply, but how soon can she do that. And how can she change her personal circumstances