Would I enter Maria Watson or Maria <Blank>?
Thanks for the question. Here is a link from the Help Center that should assist you in how to enter names.
Women are entered with maiden names but if you do not know the maiden name it is left blank. The system is programed (when looking for hints) to look for her with her name as well as with her husbands surname so it is not necessary to use the surname of the spouse.
Hope this helps Family Search
Thank you for your question and for your dedication to the indexing program. You would enter "Maria" and mark surname field "blank".