Wife just started as an independent contractor. She was previously employed and received a W2 for this past year. She types doctors reports and gets paid per line. We file our taxes jointly. We were both working for this same company and each had our W4 set as single and claimed 1. We are not sure how to fill out the 1040ES

1) Since we have no idea what her income might be since the pay structure is completely different we were going to take a 2 month avg (Feb/March) and project. Is that acceptable? What happens if the next quarter her income goes up/down?

2) On the 1040ES should she pick single since my employer will continue to handle my portion of the taxes? In my eyes it wouldn't make since to pick the standard deduction as married (that would be double dipping on the tax payment side for me).

Thanks