What is a simple problem of a single and working mother that can be used as a thesis title?

I'm not sure here what you mean by a "thesis title." Are you working on an M.A. or PhD thesis? If so, you need to think of some area of research that contributes a small and focused study to an existing body of scholarship in your discipline. In general, this is something you do by consulting with your adviser after having spent several months reading deeply in your area and will be determined by your disciplinary location; sociology, social work, criminal justice, and psychology will have different approaches to this topic. Also, you need to decide whether you want to do an ethnography, a thick description of the life or an individual single mother or a small group of single mothers, a broader statistical study of a specific group of single mothers, or a theoretical study. One possible empirical study would be one of the type "Access to Child Care for Single Mothers in [name of town] in 2016."
If by "thesis title" you are attempting to develop a thesis or central claim for a short paper for a high school or introductory university writing course, you should know such a paper is termed an "argumentative paper," not a "thesis." The term thesis in such a context refers to the central claim of the paper. At this level, you are being asked to come up with an argumentative paper. Purely expository papers which simply describe something have a subject area or focus but not a "thesis." Thus, if you are looking for an argumentative thesis, you want a statement with which people could agree or disagree, not simply a one-sided claim. You might choose a topic such as "X is the most effective HUD program to help single working mothers." You would then research the various housing programs sponsored by HUD and argue about their respective merits.
https://www.hud.gov/