Dependant "Previous Name" issue

Hello All,

I am not sure, if anyone has faced this issue. please share/advice after reading.

My wife has only "First Name" field in her maiden passport filled. When we got married, she was granted her initial EC sticker with only "First Name" on it. We came and applied for a name change on her Passport in London and got her name changed to Married name.

Now, I am applying for her 2nd extension, and while filling the form online, it does asks if you were known by any other name, in the first extension i filled the paper form and left "Last name" empty.

Question is:

1) What should be filled online in "Last name" field.
2) What are the consequenses for her ILR application which is due in May 2018, if the last name feild is filled as per her educational documentation, which i will be using for her english language requirement.

Please advise.

Thanks