Firstly well done you, working, studying and being a single parent with enough care and compassion to worry about your DD's needs ahead of you own.
Secondly the most effective time of day to train is first thing in the morning before eating. It's called fasted cardio and offers the most effective weight loss because your body is consuming it's fat stores rather than burning recently consumed fuel from breakfast/lunch/dinner. Even 5 mins of jogging, fast paced walking, dancing or whatever is enough. Pop on some music first thing and have a dance/jog about the house before or whilst getting ready. Drink plenty of water. More than half the time we think we are hungry we are actually just thirsty....drink water when hunger strikes.
Thirdly diet low carbs and lean protein. Switch white bread for wholemeal, do the same for pasta and rice, buy leaner meats or trim the fat. Drink a glass of water 20-30 mins before eating it helps fill you up but also aides digestion. Snacks: snack on nuts, rice cakes etc instead of crisps and biscuits.
When buying food be more aware of the sugar content than the fat content. Whole milk is a prime example of this. Whole milk is much more beneficial for you than skimmed...skimmed milk is basically milk with all the goodness (good fat) removed. Most food that advertise as being low fat are high in sugar and sugar is worse than good fat. Obviously you want to avoid trans fats and saturated fats but certain fatty foods are good for you like nuts, oats, eggs and these are very filling/satisfying and help to prevent cravings.
Lastly instead of making radical changes, make smaller changes over a longer time period. Make changes you and your family will easily be able to stick too. Like anything diet and excercise work best when they are consistent over a long period. Also once every week/couple of weeks allow a cheat day. This is a day to look forward to when you can eat whatever you've been craving/missing and it helps you stick to a healthy diet long term because your not completely denying pleasurable foods your just regulating them.
Sorry that's long but I hope it helps. Remember small achievable goals, a little at a time makes the whole thing more manageable. 