Wanted to share additional information i found on this topic. For anyone who has I-485 pending, you can get a EAD which will allow you to get a SSN and then file the tax as dependent. This information might come handy to someone in future.
Now that my mother's Green Card and SSN is. here, i would like to file my return electronically. I had filed for the extension, since the SSN had not arrived in time. Can i still file electronically?
