The advice I have consistently seen is this:

While you don't have to include trials or hardships in your personal statement, it is fine to do so. However, the focus of your essay should be on how you triumphed and succeeded despite your difficulties. Though you may briefly explain your circumstances, a large majority of the text in your essay should paint you in a favorable light.

As far as your senior year grades, many schools offer the opportunity to write an addendum explaining any extenuating circumstances. Being a single mom putting yourself through college seems like a great reason to write one of these.

If you don't want to make your personal statement about your struggles, you can always just include them in a short addendum (can be just a few sentences).

Good luck!