Can i ask what steps you have already taken? You can try an isolation test to identify the component that is not working. But i really need to know what was your recent activity in solving the problem.
Let me do some help to you based on what I know. Well for a start, you can do some diagnostics for what might be the cause on why it is not charging.
Step 1: Try to check if the charger you are using is still operational. You can try it by trying to use it to other phones aside from your mothers Lenovo a6000
Step 2: Try to check its battery. I am not sure if Lenovo a6000 has a removable battery but if it does, you can go to a nearby celphone accessories shop and look for a similar battery such as yours and ask the sales person if they have the battery for it and if they have, you can try it out for a moment if it charge mode is becomes active,(some celphone shops allows buyers to try their accessories before actually buying it.especially those that are in the markets from outside the malls) theres a possibility that the fault is really in your battery, but if it still won't do, then the possibility is with your mum's phone itself.
Step 3: If it is with the battery's fault you can go to an expert and ask him to do something to reactivate it, ( I am not sure if it is a thing nowadays but in my previous years with old phones such as those Nokia 3310, the battery can be revive using a shock device.) But if it is not you don't have a choice but to replace it with a new one. If ever the fault is with the phone, You can bring it to the store where you have bought it. If you just bought it recently, it might still be covered with its warranty service. Or if not, there's still a lot of expert technicians who repairs smart phones for a living.