There is nothing to stop you helping her voluntarily for free but if you are paid by the company for doing so then you should declare the money received as income to the tax office.
I hope this helps.If there are any further points please reply.
and is there a limit of hours in which I can help her?
for example, if there is a business meeting, can I be present and say that I help her?
I would like to help her for free quite a lot t the beginning, but I do not need to be paid
There is no limit to the amount of time that you can help her voluntarily for free.