Mothering Sunday is one of those traditional celebrations that has its roots deep in British history. It comes from when children would leave home at an early age probably in their mid teens, and go away to work. There would be very few holidays available for them to return home to see their families. Mother's Day would be one of the few holidays when they would be able to return home to cede their mom and dad. It was in early spring, so people would often pick flowers on the walk home and present these to their mom.
You do not have to spend a lot of money on your mom to make her feel special on Mother's Day. By simply spending some quality time with her, sharing her interests, having a good chat, perhaps cooking dinner, you'll spend some really valuable time with your mom. She will probably appreciate this a lot more than expensive flowers, champagne or jewellery. That doesn't mean you shouldn't buy her something lovely to. What it does mean you have to make an effort and spend valuable time with her. She will appreciate this!