According to Proviso to Sec 139. it is mandatory to file return if the gross income before deductions exceed the taxable limit not chargeable to tax. therefore it is not necessary to file any return if the gross income before deductions doesn't exceed the taxable limit not not chargeable to tax.
Penalty would be leviable only if it is necessary to file any return otherwise not.
If d Assesee has not filed return in time it becomes a belated
return u/s 139(4) however it can b filed within 1 year from d end of the assessment year or till d end of d assessment whichever is earlier failure of which will make d assesse in default
thus she can file d return till 31/03/2010 if taxable income is below exemption limit no intrest
as per sec 271F if an assessee is required to file return u/s 139 & fail to file such return before d expiry of relevant A/y d AO may impose a penalty of rs 5000 on assessee for not filing of return. it is discretionery power of AO but if assessee is not required to file return u/s 139 then AO Can't impose penalty in any case & in case of individual assessee return is required to file only if total income before deduction u/c VI A & exemption u/s 10A, 10B & 10BA exceeds maximum amt not chargeable to tax