Ask an Immigration Solicitor. Get an Answer ASAP.
I can help you for your concerns.
You can not apply within the UK because main applicant is not living in UK.
she will have to apply from her home country.
if you are sponsor then you will have to provide your own 6 months pay slips, Bank statements.
You must have funds in your account to convince the immigration officer that you will be responsible for her living expenses in UK. You should provide invitation letter to her in which you should mention that you will provide accommodation for her stay in UK.
Main applicant must also prove that she will be back at the end of the expiry of her visa.
i hope it will help you
please give positive rating